Reported in: https://wald.intevation.org/forum/message.php?msg_id=5076&group_id=11
I can reproduce this when I send a mail with an outlook.com account and look into the sent messages folder. This is similar to exchange <> exchange transfer on the same exchange server. The body is available unencrypted additionally to the PGP/MIME attachment.
This is a regression as I have mails in there where the body was properly wiped.