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Trust S/MIME Signing Certificates in Outlook

By default Hermes SEG uses self-signed S/MIME certificates for encryption and signing. E-mail clients such as Outlook do not trust those self-signed certificates. In Outlook, emails signed with the self-signed certificates show an invalid digital signature error (Figure 1).

Figure 1


In order to have Outlook trust the certificates, click on the yellow triangle to the right of the e-mail in question (Figure 2).

Figure 2


In the resultant Digital Signature pop-up window, click on the Details button (Figure 3).

Figure 3


In the resultant Message Security Properties pop-up window, click on the Signer e-mail address and then click on the Edit Trust button (Figure 4).

Figure 4


In the View Certificate pop-up window, in the Trust tab, under the Edit Trust section, select Explicitly Trust this Certificate and click OK (Figure 5).

Figure 5


Close and re-open the e-mail in question and the yellow triangle is now replaced with a red ribbon indicating that the Digital Signature is trusted (Figure 6).

Figure 6