I’ve been digging into the mime handling code. In SMTP, attachments appear to be encrypted independently and prior to any encryption of the email itself. When it comes to time to decrypt the attachment, yes, tcl mime hands off to trf, and when trf is asked to decrypt attachments in mime email, it hands off to trfcrypt.
trfcrypt is an add-on for trf, and it looks like we don’t include it.
I would assume that was decision made many years ago in order to be compliant with regulations on the transfer of cryptography over international borders. I’m having trouble finding any examples of trfcrypt or a crypt.dll anywhere in our legacy materials/downloads.