I am not receiving e-mails that are using my custom e-mail when people send me e-mails using GPG Tools. I have my private pgp key to decrypt on my Gmail account, but they don't seem to be handled at all by Jira Service Desk. Unencrypted e-mail forward and come through just fine, and are JSD will reply as expected.
I would expect that I would have the subject reflected in the Jira Service Desk ticket, but that the encrypted body would just be an .asc attachement (other attachments appear in comments). But, that is not happening.