Email Policies

Disclaimers

Disclaimers

Pro Edition feature. Maps to Email Policies > Disclaimers (view_disclaimers.cfm, edit_disclaimer.cfm, disclaimer_delete.cfm).

Hermes appends a configurable disclaimer to outbound mail at the gateway, with two scopes:

Scope Sender match Use case
Domain All senders in @example.com Default org-wide compliance/legal language
Relay Recipient Specific full address (e.g. vendor@example.com) Per-relay-user override for tenants with extra regulatory language

Most-specific match wins: a relay-recipient match is used before the domain default.

Pipeline placement

Disclaimers are applied at SMTP receive time by the hermes_body_milter container, which Postfix consults as a milter alongside OpenDKIM and OpenDMARC.

External MTA / MUA submission
        │
        ▼
Postfix smtpd
   ├─ smtpd_milters chain (in order):
   │   1. OpenDKIM            (signs/verifies)
   │   2. OpenDMARC           (DMARC policy)
   │   3. hermes_body_milter  (THIS — disclaimers, signatures, banners)
   ▼
content_filter → Amavis    (unmodified path; sees the body milter's output)
   ▼
Ciphermail              (server-side S/MIME or PGP, if configured)
   ▼
Postfix :10026          (OpenDKIM signs the final composed body here)
   ▼
external

Body modification happens at smtpd time, before content_filter routes to Amavis. By the time Amavis sees the message, the disclaimer is already baked in. Amavis processes a normal-looking message; no internal-state coupling, no temp-file races.

OpenDKIM's outbound signing fires at the :10026 re-injection — after both the body milter and Ciphermail. Hermes' own DKIM therefore always covers whatever the recipient ultimately receives. Ciphermail's server-side crypto also covers the disclaimer because Ciphermail runs after the milter.

Behavior with S/MIME, PGP, and DKIM-signed mail

The behavior depends on who signed/encrypted the message and when in the pipeline.

Server-side: signed/encrypted by Ciphermail — disclaimer is applied

Ciphermail runs after the body milter. Mail arrives at the milter as plaintext, the disclaimer is appended, then Ciphermail signs or encrypts the modified body. The recipient sees a valid signature and the disclaimer. No conflict.

Client-side: signed/encrypted by the user's MUA — disclaimer is skipped

Mail signed in Outlook (S/MIME) or Thunderbird+Enigmail (PGP) arrives at the gateway with the cryptographic envelope already sealed. Modifying the body would either invalidate the signature or mangle the ciphertext.

The body milter detects the following patterns in the headers (or first 32 KB of the body) and exits unchanged when any matches:

Pattern matched Meaning
Content-Type: multipart/signed; protocol="application/pkcs7-signature" S/MIME detached signature
Content-Type: application/pkcs7-mime S/MIME opaque-signed or enveloped
Content-Type: multipart/signed; protocol="application/pgp-signature" PGP/MIME detached signature
Content-Type: multipart/encrypted; protocol="application/pgp-encrypted" PGP/MIME encrypted
-----BEGIN PGP SIGNED MESSAGE----- in body PGP inline-signed
-----BEGIN PGP MESSAGE----- in body PGP inline-encrypted

When any of those match, the body is left untouched, the signature stays valid, the user's legal-text expectations are preserved (their MUA template is already in the body), and the gateway gets out of the way.

Operational consequence. A site whose users sign client-side will not get gateway disclaimers on those specific signed messages — by design. If org-wide legal text on all outbound is mandatory, the only safe pattern is server-side signing in Ciphermail with the disclaimer applied first.

DKIM: Hermes-signed mail is fine; upstream-signed mail is skipped

OpenDKIM signs at the Postfix :10026 re-injection step — after the body milter. So Hermes' own DKIM signature always covers the recipient's view of the message (with disclaimer baked in). No conflict.

The risk is mail that arrives at Hermes already DKIM-signed by an upstream MTA — typically a relay user whose own mail server signs before forwarding through us. Modifying that body would invalidate the upstream signature at the recipient.

The body milter treats a pre-existing DKIM-Signature: header the same way as a sealed S/MIME or PGP envelope and skips the disclaimer. Since Hermes' own DKIM signs at :10026 (downstream of this milter), any DKIM-Signature header present at the milter's point in the pipeline came from somewhere upstream of Hermes.

Reply-chain handling — no dedup, by design

The milter does not detect or skip messages that already carry a previous disclaimer in their quoted history. Every outbound message gets a fresh disclaimer applied — including replies inside a long thread.

This matches industry norm: commercial server-side disclaimer / signature platforms (Exclaimer, Crossware, CodeTwo, Microsoft 365 transport rules) all stamp every outbound without dedup. The reasoning:

Earlier iterations of #214 included a sentinel-marker dedup mechanism ([HD] / <!-- HERMES_DISCLAIMER_V1 -->). That was removed during DEV testing in favor of the industry-norm pattern.

Position: append vs prepend

The schema and UI both expose position = append | prepend, but v1 honors append only. Prepend is tracked as a v2 enhancement.

Failure semantics

The body milter is graceful-degradation by design. Postfix's milter_default_action = accept means:

In every failure case, mail keeps flowing. Worst case is a missed disclaimer, never lost mail. Compare the legacy "modify in amavis hook" approach (#214 Phase 3 v1, retired) which silently dropped messages when the in-place body modification desynced amavis's internal state.

Files generated on save/delete

The CFML include inc/disclaimer_write_and_reload.cfm runs after every save or delete and rewrites the entire on-disk state from the disclaimers table:

/etc/hermes/body_milter/disclaimers/disclaimer_by_sender   sender → option map
/etc/hermes/body_milter/disclaimers/files/<option>/
    body.txt          plain-text disclaimer
    body.html         html disclaimer (may have <img src="cid:..."> refs)
    images/
        1.png         per-disclaimer inline images (#230)
        2.jpg
        ...

Where <option> is domain_<safe> or relay_<safe> (non-alphanumeric chars in the source key are replaced with _).

Each disclaimer gets its own subdirectory. The files directory is wiped (per-option subdirectories deleted recursively, but the parent files/ directory and its .gitkeep are preserved) and rewritten on every save. There is no incremental update — this guarantees deleted rows and renamed scope keys never leave stale files (or stale image binaries) behind.

No reload step needed. The body milter mtime-watches each map file on every message and reloads when it changes. The CFML cffile write to the map file is enough to make the change take effect on the next message processed by the milter.

Inline images (#230)

Admins can paste or upload images directly into the Quill editor when authoring a disclaimer. Supported formats: PNG, JPEG, GIF. SVG and WebP are explicitly rejected (security and recipient-compatibility reasons). Limits enforced at save time:

If any limit is exceeded, the save is rejected with a specific error explaining what failed. Admins can reduce image count or size and re-save.

How it works:

  1. Quill embeds pasted/uploaded images as base64 inline <img src="data:image/...;base64,..."> in the HTML body. The base64 representation is what's stored in the disclaimers.body_html column.
  2. At save time, the regenerator parses body_html for data: URLs, decodes each base64 blob, writes the binary as <option>/images/<N>.<ext>, and rewrites the HTML in <option>/body.html to use <img src="cid:disclaimer_<option>_img_<N>"> references.
  3. At message-send time, the body milter reads body.html, walks <img src="cid:..."> references, and attaches each referenced image as an image/<format> MIME part with Content-ID: <disclaimer_<option>_img_<N>> and Content-Disposition: inline.
  4. The milter wraps the message as multipart/related so the recipient MUA resolves cid references against the inline parts.

MIME structure transformation (representative example):

Original outbound:
  multipart/alternative
    text/plain
    text/html (no images)

After milter (with disclaimer including 1 image):
  multipart/related
    multipart/alternative
      text/plain  (with text disclaimer appended; images omitted from text)
      text/html   (with html disclaimer + <img src="cid:...">)
    image/png
      Content-ID: <disclaimer_..._img_1>
      Content-Disposition: inline

This structure renders inline in all major MUAs (Gmail, Outlook, Apple Mail, Thunderbird, mobile clients).

The plain-text version of the disclaimer omits images entirely — base64 inline images don't translate to text, and recipients viewing the message in plain-text mode see the disclaimer text without any image markers.

Hermes' own DKIM signature covers the modified body (including the multipart/related wrap and image parts), because OpenDKIM signs at the postfix :10026 re-injection step — downstream of the body milter. The signature validates against what the recipient receives.

Auto-derive of plain-text part

The Quill editor on edit_disclaimer.cfm drives body_html. By default the plain-text part shipped to recipients with a non-HTML MUA is auto-derived from the HTML on save: <br>, </p>, </li> become newlines, all other tags are stripped, runs of 3+ newlines collapse to 2.

Admins who need character-perfect plain text different from the auto-strip (e.g. for regulated industries) can toggle Edit plain-text version separately to expose a second editor. When set, body_text is shipped verbatim instead of derived.

Disabled rows

Rows with enabled = 0 are skipped entirely on regen — no files written, no map entry. The milter never matches that scope until the row is re-enabled.

Internal-only mail

v1 does not suppress disclaimers for internal-only mail (sender + all recipients in @local_domains). Domain disclaimers will be applied to internal mail in the same domain. If this is a problem for your install, file a feature request to add an internal-only bypass.

Why a separate milter and not an amavis hook

Earlier #214 iterations attempted to dispatch the disclaimer from inside an amavisd-new Custom.pm before_send hook, calling altermime via system() on the temp file amavis was managing. amavisd-new 2.13 caused two problems: the legacy @disclaimer_options_bysender_maps dispatch path was removed (variables still parse but no code reads them), and the before_send hook documentation says "may modify mail" but in practice in-place body modification desynchronizes amavis's internal MIME state and silently loses mail.

The body milter approach moves the body-modification step out of amavis entirely. amavis's role is unchanged from before #214 ever existed; the milter sits in postfix's smtpd_milters chain alongside OpenDKIM and OpenDMARC, the same architectural pattern Hermes already uses for body-touching policy enforcement. amavis is fully decoupled from the disclaimer feature, which means amavis upgrades and the disclaimer feature evolve independently.

This same milter container is intended to host:

Each is a Modifier subclass in /usr/local/bin/hermes-body-milter registered in the MODIFIERS list. The dispatcher is unchanged.

External Banner

External Banner

Maps to Email Policies > External Banner (view_external_banners.cfm, edit_external_banner.cfm, external_banner_delete.cfm). Available on both Community and Pro editions — phishing protection is a baseline security feature, not a Pro upsell.

Hermes prepends (or optionally appends) a warning banner to inbound mail from external senders destined for a local recipient. The banner is injected into the message body itself, so every MUA — webmail, Outlook, Apple Mail, mobile clients — renders it without relying on transport rules or recipient-side configuration. Tracked as #228.

Scope

Scope Recipient match Use case
System default All recipient domains (no override) Single banner used everywhere; recommended starting point
Per-recipient-domain Specific local mailbox domain (e.g. legal.example.com) Different copy or compliance language for one domain

Resolution at message time, in the body milter's ExternalBannerModifier:

  1. Look up the first local recipient's domain in /etc/hermes/body_milter/banners/banner_by_recipient_domain.
  2. If a matching row exists, use it.
  3. Otherwise fall back to the _default system-wide entry.
  4. Otherwise no banner is applied.

Only the first local recipient is consulted — mixed-domain envelopes get the banner of the first local recipient encountered. This keeps the modification deterministic regardless of envelope ordering.

The recipient_domain field is locked after creation. Delete and re-create the row to change scope.

What counts as "external"

The body milter uses Postfix's /etc/postfix/relay_domains file as the source of truth for "local". A message is considered inbound from an external sender when:

Internal-to-internal mail (sender + all recipients local) is classified as direction = internal and the banner is not applied. There is no separate allowlist of "trusted partner" external senders today — every external sender to a local recipient triggers the banner if one is configured for that recipient's domain.

Pipeline placement

The banner is injected at SMTP receive time by the hermes_body_milter container, the same container that emits outbound disclaimers (disclaimers.md) and organizational signatures (organizational-signatures.md). The milter listens on inet:hermes_body_milter:8893 and Postfix consults it as part of smtpd_milters.

Inbound external MTA
        |
        v
Postfix smtpd
   +- smtpd_milters chain (in order):
   |    1. OpenDKIM            (verifies upstream DKIM signature)
   |    2. OpenDMARC           (DMARC policy + ARC verification)
   |    3. hermes_body_milter  (THIS -- banner prepended here)
   |       --> Authentication-Results header has already been written
   |           by OpenDKIM/OpenDMARC BEFORE the banner touches the body
   v
content_filter --> Amavis    (sees the banner-prepended body)
   v
Ciphermail              (server-side S/MIME or PGP, if configured)
   v
Postfix :10026          (multi-instance OpenDKIM re-signs the final body)
   v
Local delivery (Dovecot LMTP)

Key ordering points:

Behavior with signed and encrypted mail

The modifier inherits the same skip rules as Disclaimers for sealed envelopes:

Pattern matched Meaning Banner action
Content-Type: multipart/signed; protocol="application/pkcs7-signature" S/MIME detached Skip
Content-Type: application/pkcs7-mime S/MIME opaque/enveloped Skip
Content-Type: multipart/signed; protocol="application/pgp-signature" PGP/MIME detached Skip
Content-Type: multipart/encrypted; protocol="application/pgp-encrypted" PGP/MIME encrypted Skip
-----BEGIN PGP SIGNED MESSAGE----- in body PGP inline-signed Skip
-----BEGIN PGP MESSAGE----- in body PGP inline-encrypted Skip
Pre-existing DKIM-Signature: header on inbound mail Upstream DKIM signed Modify anyway (see below)

The corresponding flags on ExternalBannerModifier are skip_on_signed = True, skip_on_pgp_inline = True, skip_on_dkim = False.

Why the banner does NOT skip on upstream DKIM

About 95% of inbound mail today carries a DKIM-Signature: header. If the banner skipped on DKIM, the feature would be effectively inert — the warning would only land on the unsigned minority that needs it least.

Hermes already records the upstream DKIM verdict in Authentication-Results: before modifying the body. Recipients overwhelmingly read mail through Dovecot/IMAP and the recipient MUA does not re-verify upstream DKIM. The banner is therefore safe in the common case.

The narrower edge case — a recipient who forwards Hermes-banner'd mail to a downstream MX that does re-verify upstream DKIM — is addressed by ARC sealing (#229). Hermes' ARC seal at :10026 records cv=fail for the upstream chain (because we modified the body), but the seal itself is mathematically valid and the downstream MX can trust Hermes' ARC verdict if Hermes is on its allowlist. See ARC Settings for the full discussion of the cv=fail-by-design pattern.

Operational consequence. Banner injection breaks the original sender's DKIM body hash and any upstream ARC body hash. This is by design. Hermes is the authoritative auth boundary for the domains it relays; customer downstream MX servers must allowlist Hermes and accept its delivered mail without re-running DKIM/SPF/DMARC/ARC. A downstream MX that re-verifies upstream auth on mail Hermes forwards is misconfigured — cross-ref ARC Settings, DKIM Settings, and DMARC Settings.

Position: prepend vs append

Position Behavior Recommendation
Top (prepend) Banner becomes the first child of the message body (above any quoted history) Industry standard — users see the warning before reading any content
Bottom (append) Banner is appended after the user-visible body Available for sites that prefer it; rarely used

Both positions are implemented end to end (unlike Disclaimers, where only append is honored in v1). HTML prepend is done with BeautifulSoup: the banner fragment is inserted as the first child of <body> when present, otherwise prepended to the root.

Templates

Banners use a server-side template gallery, not a free-form WYSIWYG editor. Quill 2.x's HTML normalization strips inline styles that Gmail and Outlook need (the same problem hit on Organizational Signatures #226 Phase 2 and on this feature), so admins pick a template and fill in form fields; the server renders pixel-perfect HTML at save time.

Bundled templates (each inc/external_banner_templates/<key>.cfm):

Template key Display name When to pick it
warning_yellow Warning Yellow Default. Yellow background with orange accent. Matches Microsoft 365 / Mimecast banner style most users recognize
critical_red Critical Red Red background, white text. Phishing-prone industries or post-incident periods where alert level needs to be raised
subtle_info Subtle Info Light gray with blue accent. Less alarming for high-volume inbound (support/sales) where alert fatigue is a concern
plain_text Plain Text Bold prefix + text, no background or border. Maximum cross-MUA compatibility, including text-only clients

All four templates expose the same field set:

Field Type Default Notes
prefix text [EXTERNAL] Short tag rendered bold at the start. Plain ASCII recommended for Outlook
headline text "This message originated from outside your organization." First line, regular weight
body text "Do not click links or open attachments unless you recognize the sender..." Second line, smaller text
show_learn_more checkbox false Reveals the next two fields
learn_more_url url empty Optional link to internal phishing-awareness training or wiki
learn_more_label text "Learn more about phishing" Visible label for the learn-more link

All templates emit table-based HTML with bgcolor= attributes so Outlook (which strips inline CSS but honors deprecated HTML attributes) renders the banner correctly. Inline styles are belt-and-suspenders for Gmail, Apple Mail, and mobile clients.

The edit page renders a live preview in an iframe via inc/render_external_banner_preview.cfm so the admin sees exactly what save_external_banner_action.cfm will store.

Files generated on save/delete

inc/external_banner_write_and_reload.cfm runs after every save or delete and rewrites the entire on-disk state from the external_banners table:

/etc/hermes/body_milter/banners/banner_by_recipient_domain
    <recipient_domain>\t<option>
    _default\t<option>          special key, system-wide fallback

/etc/hermes/body_milter/banners/files/<option>/
    body.txt          plain-text banner (auto-derived at save)
    body.html         pre-rendered html banner
    position          "prepend" or "append" sidecar file
    images/           per-banner inline images (#230 cid pattern)
        1.png
        2.jpg
        ...

Where <option> is:

The files/ subdirectory is wiped on every regen (per-banner subdirs deleted recursively; the .gitkeep is preserved). This guarantees deleted rows and renamed scopes never leave stale files behind.

No reload step needed. The body milter mtime-stats each map file on every message and reloads automatically when its mtime changes. The CFML cffile write to the map file is enough to make the change take effect on the next message.

Plain-text part

The HTML body stored in external_banners.body_html is rendered server-side from the chosen template. The plain-text counterpart in body_text is auto-derived at save time:

The plain-text version is shipped to recipients viewing the message as text/plain. Inline images are omitted from the plain-text part — data URLs don't translate to text and recipients in text mode see the banner copy without image markers.

Inline images (#230)

The banner modifier inherits the #230 cid inline-image pattern from Disclaimers. If a template's HTML contains <img src="cid:banner_<option>_img_<N>"> references, the body milter:

  1. Loads matching images/<N>.<ext> files from the option directory.
  2. Attaches each as an image/<format> MIME part with Content-ID: <banner_..._img_N> and Content-Disposition: inline.
  3. Wraps the message as multipart/related so MUAs resolve cid references against the inline parts.

The cid prefix is banner_ so banner images cannot collide with disclaimer_ or signature_ cids inside the same composed message (the three modifiers can all add images to the same outbound; namespacing keeps them separate).

The bundled templates do not currently use inline images — banners are pure text. The infrastructure is present for future template additions (logo, warning icon, etc.).

Failure semantics

The body milter is graceful-degradation by design. Postfix's milter_default_action = accept means:

In every failure case, mail keeps flowing. Worst case is a missed banner, never lost mail. Compare the legacy "modify in amavis hook" approach (#214 Phase 3 v1, retired) which silently dropped messages when the in-place body modification desynced amavis's internal state.

Disabled rows

Rows with enabled = 0 are skipped entirely during regen — no files written, no map entry. The milter never matches that scope until the row is re-enabled. Useful for staging copy changes before going live (build the new row disabled, preview it on edit_external_banner.cfm, flip the switch when ready).

Schema

CREATE TABLE IF NOT EXISTS external_banners (
  id               int(11)         NOT NULL AUTO_INCREMENT,
  recipient_domain varchar(255)    DEFAULT NULL,                -- NULL = system default
  template_key     varchar(64)     NOT NULL DEFAULT 'warning_yellow',
  fields_json      longtext        DEFAULT NULL,                 -- form values for re-edit
  body_text        longtext        DEFAULT NULL,                 -- auto-derived plain text
  body_html        longtext        NOT NULL,                     -- pre-rendered html
  position         enum('prepend','append') NOT NULL DEFAULT 'prepend',
  enabled          tinyint(3)      NOT NULL DEFAULT 1,
  updated_at       timestamp       NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
  PRIMARY KEY (id),
  UNIQUE KEY uk_recipient_domain (recipient_domain)
);

The UNIQUE KEY on recipient_domain ensures only one row per recipient domain (and at most one system-default row where recipient_domain IS NULL). The fields_json blob stores the original form values so reopening the editor restores exactly what the admin typed; body_html is the rendered output the milter actually ships.

Verifying it works

The banner appears in the message body, so the easiest verification is to send an inbound message from an external account to a local mailbox and view the result in any MUA (webmail, Outlook, Apple Mail). Beyond that:

Link Guard

Link Guard

Pro Edition feature. Maps to Email Policies > Link Guard (view_linkguard.cfm, inc/linkguard_write_and_reload.cfm).

Link Guard provides time-of-click protection for inbound mail. Links in delivered messages are rewritten to point at a Hermes redirect endpoint; when a recipient clicks, Hermes evaluates the destination's reputation at that moment and decides — instantly — whether to allow, warn, or block. This closes the gap that delivery-time scanning misses: a link that is clean when the message arrives but is weaponized hours or days later.

Protection travels with the link. It works in the inbox, after a forward to a colleague, or when the message is opened days later on a phone — because the verdict is computed on click, not on delivery.

Components

Component Role
hermes_body_milter Rewrites inbound links at SMTP receive time (LinkGuardModifier) and restores original links on outbound replies/forwards (LinkGuardRestoreModifier).
hermes_linkguard The verdict + redirect engine. Serves the public /lg/ click endpoint and a console-only management API. Holds the operational SQLite store (verdict cache, feeds, click log).
hermes_nginx Reverse-proxies /lg/ from the public console host to the Link Guard container's public port.
Admin console view_linkguard.cfm page; on save, inc/linkguard_write_and_reload.cfm pushes settings, scope, URL rules, and HMAC keys to the engine and reloads the milter maps.
Port Surface Exposure
8894 (public) GET /lg/?t=<token>, POST /lg/proceed, GET /healthz nginx-proxied; reachable by recipients clicking links
8895 (mgmt) POST /api/config, POST /api/keys, POST /api/feed-refresh, GET /api/stats console-only; never exposed publicly

The public surface can never push config or read keys; the management surface is never reachable from the internet.

Pipeline placement

INBOUND (rewrite)                          OUTBOUND (restore)
External MTA ──► Postfix smtpd             User reply/forward ──► Postfix smtpd
        │                                          │
        ▼                                          ▼
   smtpd_milters chain:                       smtpd_milters chain:
     1. OpenDKIM                                1. OpenDKIM
     2. OpenDMARC                               2. OpenDMARC
     3. hermes_body_milter                      3. hermes_body_milter
          └─ LinkGuardModifier:                      └─ LinkGuardRestoreModifier:
             rewrite links ──► /lg/ token              unwrap /lg/ tokens ──► original URLs
        │                                          │
        ▼                                          ▼
   Amavis ──► Ciphermail ──► deliver           Amavis ──► deliver to external

Rewriting happens at smtpd time, before content filtering. Hermes' own DKIM signs at the Postfix :10026 re-injection (downstream of the milter), so the signature always covers the rewritten body the recipient receives. Inbound mail that arrives already DKIM-signed, S/MIME-signed, or PGP-sealed is skipped — the same envelope-detection logic the disclaimer feature uses — so Link Guard never breaks an existing signature.

The click flow

Recipient clicks rewritten link
        │
        ▼
GET https://<console-host>/lg/?t=<token>   (nginx ──► linkguard :8894)
        │
        ├─ token invalid / expired ──► block page
        ▼
   resolve original URL from token
        │
        ▼
   verdict pipeline (see below) ──► {clean | suspicious | malicious}
        │
        ▼
   admin action for that tier:
     clean      ──► 302 redirect to the real URL   (default)
     suspicious ──► warning interstitial (resolved host shown; user may proceed)
     malicious  ──► block page (hard block, or block_override allowing proceed)

Every click is logged (recipient domain, URL hash, resolved host, verdict, source, action taken, client IP) for the reporting dashboard.

Verdict pipeline

verdict.resolve(url, recipient_domain) evaluates layers in precedence order and returns the first match:

# Layer Result Notes
1 Admin blocklist malicious Operator-curated, console-managed
2 Admin allowlist clean Operator-curated; trumps feeds and heuristics
3 Verdict cache cached result Avoids re-running heuristics / re-hitting external APIs
4 Open-redirect extraction escalate Embedded target in an open-redirect param / nested URL is resolved and inherits its verdict (no fetch)
5 Local feeds malicious URLhaus / OpenPhish, stored in SQLite; only ever escalate
6 Heuristics suspicious Lookalike/punycode, IP-literal host, @ in authority, known shorteners, excessive subdomains, abused cloud-storage/redirector hosts
7 GSB / VirusTotal malicious Optional, admin-supplied keys; string-reputation lookups, cached. Also escalates a warn-tier (step 6) link to a hard block when flagged
8 Guarded redirect-follow escalate Optional (admin toggle): follow the 30x chain under SSRF guards, verdict the final destination; also runs proactively on a step-6 warn so a malicious destination becomes a hard block
9 Default clean Nothing flagged it

Steps 1–7 never fetch the target URL — every reputation check sends the URL only as a string (Google Safe Browsing, VirusTotal). The only layer that makes an outbound request is the optional guarded redirect-follow (step 8), and only when an admin enables it; every hop is SSRF-fenced (see Redirect detection below). Local feeds only ever escalate a link to malicious; they never auto-allow.

URL shorteners are flagged suspicious (warn), not blocked — a shortener hides its real destination, which is exactly what time-of-click protection exists to surface. The warning interstitial shows the resolved host so the user can make an informed choice. The shortener set is a curated list of generic, anyone-shortens-anything services (referenced from the maintained PeterDaveHello/url-shorteners list); branded corporate shorteners (aka.ms, amzn.to, a.co, adobe.ly, …) are deliberately excluded so legitimate branded short links don't warn-fatigue users. When follow_redirects is enabled, the real destination of any shortener is resolved regardless. VirusTotal requires ≥2 vendors flagging a URL before it counts as malicious, to cut false positives.

Verdict tiers and actions

Each verdict tier maps to an admin-configurable action:

Tier Setting Default action Behavior
clean action_clean redirect 302 straight to the destination
suspicious action_suspicious warn Interstitial; user may proceed
malicious action_malicious block Block page

Available actions: redirect / allow (pass through), warn (interstitial with proceed), block (hard block, no proceed), block_override (block page that allows an explicit proceed).

A hard block can never be bypassed. POST /lg/proceed re-resolves and re-authorizes the verdict server-side — only a warn tier, or a block_override tier with the override flag, is allowed to continue. A user cannot escape a hard block by replaying the proceed request.

Redirect detection

Attackers increasingly chain through reputable hosts — storage.googleapis.com, firebasestorage.googleapis.com, *.web.app, Azure *.blob.core.windows.net, Cloudflare *.r2.dev / *.pages.dev, and classic open redirectors like google.com/url?q=… — because the host reputation is clean, so a string-only check passes the link through. Link Guard adds three layers to catch this "living off trusted services" pattern.

Open-redirect extraction (always on, no fetch)

The engine scans a link's query and fragment (raw, once-, and twice-URL-decoded) for an embedded http(s):// target on a different host than the redirector — the real destination of …/url?q=https://evil.example. That embedded target is re-run through the verdict pipeline (string-only); if it is suspicious or malicious, the original link inherits the verdict (source = redirect, detail open-redirect -> <host>). A benign embedded URL is a no-op. No outbound request is made.

Abused-host heuristic (always on, no fetch)

Cloud-storage and app-hosting hosts commonly abused to host or bounce to phishing are flagged suspicious (warn) in the heuristics layer, so the user gets the interstitial and the resolved host instead of a silent redirect. Gated by flag_cloud_storage (default on). The match is suffix-based (host == suffix or host ends with .suffix).

The list is an operator-managed table (linkguard_abused_hosts), shipped pre-seeded with a curated baseline — there is no authoritative machine-readable feed of "abused hosting platforms" (the actual-bad URLs are what the URLhaus / OpenPhish feeds cover), so the seed is hand-curated from public abuse research (Trustwave SpiderLabs, Proofpoint, Netskope, Phishing.Database). It covers object storage (storage.googleapis.com, firebasestorage.googleapis.com, firebaseapp.com, web.app, appspot.com, blob.core.windows.net, s3.amazonaws.com), edge/static-site hosting (r2.dev, pages.dev, workers.dev, github.io, netlify.app, vercel.app, herokuapp.com, onrender.com, surge.sh), free site builders (weebly.com, wixsite.com, 000webhostapp.com), and tunneling services (trycloudflare.com, ngrok.io, ngrok-free.app).

Manage it from the Abused / redirector hosts card on the Link Guard page:

Add/delete in this card applies immediately — the handler regenerates the engine's config.json on each change (same as the URL-rules and domains cards), so there's no separate Save for table edits. The flag_cloud_storage master switch and the other settings live in the settings card and take effect on its Save & reload settings button.

Guarded redirect-follow (optional, the one fetch layer)

When follow_redirects is enabled, the engine — at click time, after the string layers — follows the HTTP 30x redirect chain and verdicts the real destination, catching a trusted-host link that issues a server-side redirect to phishing (the storage.googleapis.com → phishing case). This is the only layer that makes an outbound request, so every hop is fenced (_safe_to_fetch):

Each followed hop is verdicted string-only (a follow never recurses into another follow). If the chain reaches a suspicious/malicious destination, the link inherits that verdict (source = redirect, detail redirect chain -> <final host>). A follow failure (timeout, guard stop, HEAD not allowed) fails closed for the follow — the link keeps whatever verdict the string layers produced; a click is never blocked by a follow error.

Proactive on warn-tier links. A shortener or abused-host link is flagged suspicious by the heuristics layer (step 6), which is before the follow layer in precedence. When follow_redirects is on, those warn-tier links are also followed at that point — proactively, during the verdict, not on "Continue":

So with redirect-following enabled, a storage.googleapis.com / shortener link that actually bounces to phishing becomes a block, while one that resolves somewhere benign stays an informative warn. The verdict (block or warn) is cached, so the follow runs at most once per link per cache-TTL.

SSRF posture. Steps 1–7 never fetch the target. Enabling follow_redirects is a deliberate trade: it resolves redirect chains a string check cannot, at the cost of one guarded outbound request per uncached click (latency) and a controlled egress surface. The residual DNS-rebinding window (resolve-then-connect) is accepted for this release. Leave it off to preserve the zero-fetch guarantee; the two no-fetch layers above still run.

Out of scope for this release: following JavaScript or <meta> refresh redirects, which require fetching and parsing the page body — tracked as a later enhancement.

Tokens — stateful v2 (default) with stateless v1 fallback

v2 — stateful (default). The token is just 2.<128-bit opaque id>. The milter writes the mapping id → {original_url, recipient_domain, expiry} to a shared SQLite store (url_map.db) on the linkguard_data volume; the Link Guard container reads it. Because the token itself is tiny, there is no link-length limit — every link is protected regardless of how long the original URL is. This closes the v1 over-length fail-open gap (see below).

v1 — stateless (fallback + in-flight). The token is a self-contained HMAC signature: 1.<recipient_domain>.<url>.<expiry>.<signature>. The milter mints a v1 token if the shared store is unavailable (e.g. off-box deployment, or transient DB contention), so mail flow never depends on the store. v1 tokens already in delivered mailboxes continue to verify until they age out via the token TTL.

The milter's mint/verify logic is a byte-for-byte mirror of the container's lg_token.py, so the container verifies exactly what the milter mints. The url_map.db store uses a rollback journal (not WAL), so the container can read it cross-container without a -shm file.

Why v2 exists. Under v1, a URL longer than the inline cap was left unprotected (the original link was passed through unrewritten). An attacker could pad a URL past the cap to dodge Link Guard entirely. v2's short opaque id removes the length dependency, so nothing is ever skipped. The max_inline_url setting is now a fallback-only bound for the v1 path.

restore_outbound (default on) unwraps Link Guard tokens back to the original URLs on outbound mail — when a recipient replies to or forwards a protected message, the quoted history shows the real links again, not /lg/?t=... redirects. This keeps conversations readable and prevents Hermes redirect URLs from leaking to external parties. (Microsoft 365 was verified not to strip the tokens on manual replies, so restoration is the correct default.)

HMAC key rotation

The signing key for v1 tokens is rotatable from the console. Rotation keeps a current + previous overlap: newly minted tokens use the current key, while tokens signed with the previous key still verify until they age out. The teardown on a Pro license lapse blanks only the dispatch maps and never the keys, so in-flight links keep resolving and a renew resumes minting with the same key.

Settings reference

Settings live in the parameters2 table under module = 'linkguard' (not system_settings). On save they are pushed to the engine via POST /api/config.

Setting Default Meaning
enabled 0 Master on/off for Link Guard
redirect_base_url (console host) Public base URL for /lg/ links
action_clean redirect Action for clean verdicts
action_suspicious warn Action for suspicious verdicts
action_malicious block Action for malicious verdicts
restore_outbound 1 Unwrap tokens on outbound replies/forwards
token_ttl_days 14 How long a rewritten link stays valid
max_inline_url 4000 Fallback-only length bound for v1 stateless tokens
rate_limit_per_min 120 Per-client-IP rate limit on /lg/
flag_cloud_storage 1 Flag abused cloud-storage/redirector hosts as suspicious (warn)
follow_redirects 0 Follow 30x redirect chains at click time (guarded outbound fetch)
follow_max_hops 5 Max hops to follow when follow_redirects is on
cache_ttl_clean_hours 24 Verdict cache lifetime — clean
cache_ttl_suspicious_hours 6 Verdict cache lifetime — suspicious
cache_ttl_malicious_hours 168 Verdict cache lifetime — malicious
feed_urlhaus_enabled 1 Pull the URLhaus blocklist feed
feed_openphish_enabled 1 Pull the OpenPhish blocklist feed
feed_refresh_minutes 60 Feed refresh interval
gsb_enabled / gsb_api_key 0 / — Google Safe Browsing lookups (optional key)
vt_enabled / vt_api_key 0 / — VirusTotal lookups (optional key)
clicks_retention_days 90 Click-log retention for reporting

Two additional console-managed lists drive the verdict pipeline:

Reputation feeds and optional API lookups

Setting up VirusTotal and Google Safe Browsing

Both are optional — Link Guard works without them (admin lists + feeds + heuristics + redirect-following). They add a malicious-verdict layer that checks the URL as a string against the provider (the target is never fetched). Each is enabled the moment you save its key (no Save & Reload), and a malicious result will escalate even a warn-tier link to a hard block.

Where to enter keys: Link Guard page → Reputation sources → the provider's Edit key button. Entering a key auto-enables the provider; clearing it disables and wipes the stored key.

VirusTotal (recommended):

  1. Create a free account at virustotal.com and sign in.
  2. Open your profile menu → API key, and copy it.
  3. Paste it into Link Guard → VirusTotal → Edit key.
  4. Quota: the free Public API is rate-limited (≈ 4 lookups/minute, 500/day, ~15.5k/month) and is for non-commercial use; high-volume or commercial sites need a paid Premium API key. The verdict cache (and the per-tier cache-TTL settings) is what keeps you under quota — which is why Clear verdict cache warns before re-querying. A verdict counts as malicious only when ≥ 2 vendors flag the URL.

Google Safe Browsing:

  1. In the Google Cloud Console, create (or pick) a project.
  2. APIs & Services → Library → search "Safe Browsing API" → Enable.
  3. APIs & Services → Credentials → Create credentials → API key, and copy it.
  4. Paste it into Link Guard → Google Safe Browsing → Edit key.
  5. ⚠️ Commercial-use caveat: the Safe Browsing Lookup API v4 that Link Guard uses is free but designated non-commercial only by Google, and is deprecated in favour of the paid Web Risk API for commercial use. Review Google's usage terms for your deployment. If you only want one reputation provider, VirusTotal is the simpler choice; Web Risk support may be added later.

Privacy: with either provider enabled, the clicked URL string is sent to that provider's API for the lookup. Nothing else leaves Link Guard.

Branded interstitials

The warning and block pages are served by the container (templates.py) and carry Hermes SEG branding — an inline logo, a "Hermes SEG Link Guard" header, and a footer link to hermesseg.io — rather than a generic browser error. The warning page shows the resolved host so a user can judge a shortened or suspicious link before proceeding.

Reporting and diagnostics

The admin page includes:

Verdict cache invalidation

The engine caches each URL's verdict (per-source TTL — clean 24h, suspicious 6h, malicious 168h) to avoid re-running heuristics / re-hitting APIs on every click. Two things keep it from going stale against admin edits:

Deployment — in-stack or separate host

Failure semantics

In every failure case the worst outcome is a missed rewrite or a fall-through verdict — never lost mail.

Files and data locations

Path Container Contents
/etc/hermes/body_milter/linkguard/linkguard_by_recipient_domain body_milter Scope map: protected recipient domains (_default = all)
/var/lib/linkguard/url_map.db body_milter (writer) / linkguard (reader) v2 token id → original URL store, on the shared linkguard_data volume
/opt/linkguard/app/ linkguard Engine code (server, verdict, feeds, store, token, templates)
Operational SQLite store linkguard Verdict cache, feed entries, click log

The scope map is mtime-watched by the milter and reloaded on the next message when it changes — no explicit milter reload step is needed after a console save.

Security properties (summary)

Organizational Signatures

Organizational Signatures

Pro Edition feature. Maps to Email Policies > Org Signatures (view_org_signatures.cfm, edit_org_signature.cfm, org_signature_delete.cfm).

Hermes attaches a centrally-managed signature to outbound mail at the gateway. Admins design the signature once per domain (and optionally per department); every user on that domain gets a personalized version of it on every outbound message — no per-user setup required.

Two signature types, one pipeline

Hermes ships two distinct signature concepts that run through the same body milter and the same resolver:

Type Tier Owner Storage Per-domain control
Personal Signature Community + Pro The user (in /users/2/view_signature.cfm) user_signatures table, one row per user Toggled via domains.allow_user_signatures
Organizational Signature Pro only The admin (in Email Policies > Org Signatures) org_signatures table, one row per (domain_id, department_label) One default per domain + optional per-department variants

The milter never decides which one to apply at message time. The CFML resolver picks a winner per mailbox at admin-action time and writes a precomputed sender → option map; the milter just looks up the option and applies whatever it finds.

Department names — single source of truth

Departments are defined once on the mailbox edit form (Email Server > Mailboxes > Edit Options > Personal Information > Department), as free-text values typed by the admin. There is no separate "Departments" table; a department exists as soon as one mailbox is in it.

The Org Sig form's Department field is a strict dropdown sourced from the distinct mailboxes.department values for the selected domain. This means:

The mailbox edit form's Department field is a free-text input with a <datalist> typeahead showing the same per-domain dept list. Admins can pick an existing dept (auto-completes) or type a brand-new dept name (which then appears in the dropdown next time).

If you edit an existing Org Sig whose department_label no longer matches any current mailbox (the dept was renamed elsewhere, or all mailboxes in it were reassigned), the orphan value is preserved in the dropdown with a (no mailboxes) suffix so you can still see and edit/delete the row instead of silently losing the value.

The resolver at send time does a case-insensitive trimmed match against mailboxes.department, so casing or whitespace drift across edits is forgiving even in the rare cases the dropdown is bypassed (e.g. direct SQL changes).

Resolution order

For every enabled mailbox, the resolver walks this priority chain top-down and stops at the first match:

1. Personal Signature
   └─ if domains.allow_user_signatures = 1
      AND user_signatures has an enabled, non-empty row for this mailbox
   ─> wins. option = user_<sanitized_email>

2. Department Organizational Signature
   └─ else if mailboxes.department is non-empty
      AND org_signatures has enabled = 1 row matching
          (domain_id, department_label)
   ─> wins. option = org_<row_id>

3. Domain Default Organizational Signature
   └─ else if org_signatures has enabled = 1 row matching
          (domain_id, department_label IS NULL)
   ─> wins. option = org_<row_id>

4. None
   └─ no map entry; the milter applies no signature to this sender's mail.

The chain is per-mailbox, not per-message. The resolver runs at admin-action time (see Triggers), serializes the winning option for every mailbox into one map file, and the milter consults that map at send time. There is no per-message DB query and no per-message resolution logic in the milter.

Pipeline placement

Same chain as Disclaimers (#214) — see disclaimers.md for the full Postfix / OpenDKIM / Ciphermail picture. The summarized order:

External MTA / MUA submission
        │
        ▼
Postfix smtpd
   ├─ smtpd_milters chain (in order):
   │   1. OpenDKIM            (signs/verifies)
   │   2. OpenDMARC           (DMARC policy)
   │   3. hermes_body_milter  (THIS — signatures, then disclaimers)
   ▼
Amavis  →  Ciphermail  →  Postfix :10026 (DKIM sign) → external

Inside the body milter, SignatureModifier runs before DisclaimerModifier, so the layered output on the outbound message is:

[user body]
[signature]      ← Personal or Organizational, picked by resolver
[disclaimer]     ← if a disclaimer is configured for this sender

OpenDKIM signs at the :10026 re-injection — after both modifiers — so Hermes' own DKIM signature always covers the recipient's view of the message (with signature and disclaimer baked in).

Templates

Phase 2A ships six bundled templates under /admin/2/inc/org_signature_templates/:

Template key Layout
modern_card Logo left, accent bar, contact stack right
two_column_pro Left contact, right org block + CTA button
with_social_bar Vertical contact + horizontal social-icon row
banner_with_logo Full-width banner with logo top, contact below
promo_footer Contact + bottom promotional image with link
compact_text Minimal text-only, no images, no styling

Each template is a .cfm file that declares its field schema (text / email / url / color / checkbox / image fields with optional showIf gating) and renders pixel-perfect HTML when the renderer is invoked. Admins fill in the form on edit_org_signature.cfm; the gallery thumbnail + live sandboxed-iframe preview show the result before save.

All the auto-filled fields — Name, Title, Phone, Mobile, Email ({{user.*}} from the mailbox row) plus Website and Address ({{org.*}} from the domain row) — are collapsed under an "Override auto-filled fields" toggle by default. The admin doesn't see or edit them in the common case; the placeholders flow through to the rendered HTML unchanged and the milter fills in the recipient's data at send time. Toggling the override on exposes the fields for the rare cases that need literal text instead of substitution (shared mailboxes without personal info, seasonal URL overrides, etc.).

The genuinely admin-supplied fields stay always visible — Logo, accent color, show/hide toggles for each line, CTA text and URL, social URLs, disclaimer text, and any template-specific extras (banner height, promo image, etc.). These are the admin's actual editing surface.

Net workflow: pick a template, upload a logo, set the accent color, save. Done. Every mailbox on the domain gets a fully personalized signature on its next outbound message without any per-user form input.

Templates are version-controlled in the repo, not in the database. To add a new template, drop a new .cfm file in org_signature_templates/, add its key to the registry in inc/org_signature_template_loader.cfm, and produce a 240×140 thumbnail PNG. No schema migration needed.

Placeholder substitution at send time

The signature HTML stored in org_signatures.rendered_html (and on disk in body.html) keeps {{namespace.field}} tokens literal. The body milter substitutes them per recipient at message-send time against the sender's row in sender_data.json.

Available placeholders (Phase 2B):

Token Source column
{{user.first_name}} mailboxes.first_name
{{user.last_name}} mailboxes.last_name
{{user.title}} mailboxes.title
{{user.phone}} mailboxes.phone
{{user.mobile}} mailboxes.mobile
{{user.department}} mailboxes.department
{{user.email}} mailboxes.username
{{org.name}} domains.org_name
{{org.phone}} domains.org_phone
{{org.address}} domains.org_address
{{org.website}} domains.org_website
{{org.logo_url}} domains.org_logo_path (raw URL — not cid: extracted)
{{dept.name}} mailboxes.department

Tokens whose corresponding field is empty resolve to empty string, not literal {{...}}. So if mailboxes.title is blank for a given user, the {{user.title}} token disappears cleanly from delivered mail. Unknown namespaces (anything outside user, org, dept) are also substituted to empty.

The substitution is a single regex pass on the body html and body text inside SignatureModifier.modify() — well under a millisecond per message. The map and sender_data.json both live in process memory, refreshed only when their file mtime changes.

No DB connection from the milter, ever. All resolution and substitution data is precomputed by CFML and dropped on disk; the milter consumes the file artifacts.

Triggers — when the resolver re-runs

Both signature_by_sender and sender_data.json are rewritten in full by inc/signature_regen_map.cfm on every event that could affect a winner or a substitution value:

Event Why it matters
Admin saves an Org Sig New / edited row may win for senders that previously had no match or a lower-tier match
Admin deletes an Org Sig Losers fall back to the next tier (or none)
Admin edits a domain (allow_user_signatures or org_* columns) Per-domain toggle flips the Personal-vs-Org winner; org_* values feed {{org.*}} substitution
Admin edits a mailbox (Pro fields: first_name, title, dept, etc.) {{user.*}} and {{dept.name}} substitution data changes; a department change can flip Default → Department winner
Admin adds a mailbox New sender enters resolution and may pick up a domain-default Org Sig
Admin deletes a mailbox Sender must drop from the map
User saves their Personal Signature May now win over the previously-resolved Org Sig (or vice versa if disabling)

Each trigger runs the same shared resolver. Full rebuild every time, not incremental. With low-thousands of mailboxes the rebuild is well under a second, and the simplicity rules out drift bugs ("did we forget to update X for sender Y" can't happen).

The body milter mtime-watches both files and reloads in process memory on the next message after the file changes. No SIGHUP, no IPC, no container restart.

Files generated on save

The CFML resolver writes:

/etc/hermes/body_milter/signatures/signature_by_sender   sender → option map
/etc/hermes/body_milter/signatures/sender_data.json       sender → {{token}} dict
/etc/hermes/body_milter/signatures/files/<option>/
    body.txt         plain-text signature (auto-derived from html)
    body.html        html signature with cid: refs (placeholders intact)
    images/
        1.png        per-option inline images (#230 pattern)
        2.jpg
        ...

Where <option> is user_<sanitized_email> (Personal Sig) or org_<row_id> (Org Sig). <sanitized_email> is bob.smith@example.com → bob_smith_at_example_com (@ → _at_, non-alphanumerics → _).

signature_by_sender example:

alice@example.com   org_42
bob@example.com     user_bob_at_example_com
carol@example.com   org_43

sender_data.json example (post-Lucee uppercasing — the milter normalizes to lowercase on load):

{
  "alice@example.com": {
    "USER.FIRST_NAME": "Alice",
    "USER.TITLE": "Sales Manager",
    "ORG.NAME": "Acme",
    "ORG.PHONE": "555-0100",
    "DEPT.NAME": "Sales"
  }
}

The files/<option>/ dir is wiped before re-render on every save of that row, so deleted images and renamed scope keys never leave stale binaries behind.

Inline images (cid: extraction)

Same pattern as Disclaimers (#230) — see disclaimers.md for the MIME / multipart-related details.

For Org Signatures, the cid: namespace is signature_org_<row_id>_img_<N> (Personal Signatures use signature_user_<sanitized_email>_img_<N>). Both share the milter regex cid:(signature_[\w.-]+_img_\d+), so cid: refs from either signature type are queued for inline attachment alongside any cid: refs from a domain disclaimer on the same message — no namespace collisions.

Per-template image fields use the same data: → cid: pipeline as user-pasted Personal Sig images. At admin-save time:

  1. Admin uploads the file in the form (or pastes a URL — both are handled).
  2. Browser converts the file to a data:image/...;base64,... URI via FileReader, capped at 1 MB per image.
  3. CFML renders the template; the resulting HTML carries the data: URI inline.
  4. inc/org_signature_write_files.cfm extracts each data: URI, decodes the base64 into a binary file under images/, and rewrites the html to reference <img src="cid:signature_org_<id>_img_<N>">.
  5. At message-send time the milter walks the cid: refs, attaches each image as an image/<format> MIME part with Content-ID and Content-Disposition: inline, and wraps the message as multipart/related.

{{org.logo_url}} is not cid: extracted — it's a raw URL substituted into the html as-is. Use it for hosted-elsewhere logos (your CDN, your website). Use the per-template image field for cid:-attached inline logos when you want them to render even in MUAs that block external images.

Behavior with S/MIME, PGP, DKIM-signed mail

Identical to Disclaimers — same skip rules in the same Modifier base class. Pre-signed envelopes, PGP inline, and pre-existing DKIM-Signature headers all cause the body milter to leave the message untouched.

See disclaimers.md "Behavior with S/MIME, PGP, and DKIM-signed mail" for the table of patterns and the operational consequences.

Reply-chain handling

No dedup — every outbound gets a fresh signature, including replies inside a long thread. Same industry-norm pattern Disclaimers uses; same rationale (compliance, self-contained messages, predictability). See disclaimers.md "Reply-chain handling".

Failure semantics

Same graceful-degradation contract as Disclaimers (milter_default_action = accept). If the milter container is down, if the map file is unreadable, if the modifier raises an exception, if substitution blows up — mail flows unmodified. Worst case is a missed signature; mail never gets dropped.

See disclaimers.md "Failure semantics".

Disabled rows

org_signatures.enabled = 0 causes the resolver to skip the row entirely:

Re-enabling rebuilds the on-disk files and re-points the affected mailboxes' map entries on the next regen.

Interaction with domains.allow_user_signatures

This per-domain toggle is the single switch that controls whether Personal Signatures can win over Organizational Signatures.

allow_user_signatures Personal Sig present? Result
0 yes Personal Sig ignored; resolver falls to Department / Default Org Sig
0 no Resolver falls to Department / Default Org Sig
1 yes Personal Sig wins (top of resolution chain)
1 no Resolver falls to Department / Default Org Sig

Toggle this off when you need to lock everyone into Organizational Signatures for branding/compliance — useful when a marketing or legal team wants centrally-controlled output and doesn't want individual users overriding it.

A previously-saved Personal Signature is not deleted when the toggle goes off — it just stops being resolved. Toggling back on re-activates it on the next regen.

Pro license behavior

The Org Signatures admin page is gated by session.edition EQ "Pro":

This is the same "feature stays on, admin UI locks" pattern as Disclaimers and other Pro features. If a customer wants the Pro feature actually disabled at runtime on downgrade, the path is to delete the rows or set them all to enabled = 0.

Why a separate milter and not an amavis hook

Same reasoning as Disclaimers (#214 Phase 3). amavisd-new 2.13's before_send hook silently desynchronizes amavis's internal MIME state during in-place body modification, which can drop mail. The body milter approach moves body modification out of amavis entirely; amavis is fully decoupled.

See disclaimers.md "Why a separate milter and not an amavis hook".