I’ve been setting up S/MIME on my RT instance and I manage to send encrypted emails back and forth, however I have the issue that the emails that are sent from RT are empty. The ticket log shows that an email has been sent with a p7m attachement, which I assume must contain the encrypted body of the message, however when I receive the email in my mail client, it is empty, although correctly marked as S/MIME encrypted. I have the same behavior on both outlook and thunderbird with different email addresses.
We don’t use S/MIME with our RT, but as an idea, could you send an email to a local account on the RT server (assuming its Linux or similar) and then peep into the mailbox with a text based tool (less, more, etc) to see if the attachment is included with the email? That would at least let you check what RT was generating and your local mail transfer agent on the RT server.
I haven’t managed to send an encrypted email directly with postfix but I noticed that the authentication seems to fail in the email that I get, even without signing/encryption:
