[MM3-users] Re: Problems with signed messages from Apple Mail

We have done some more investigation on this. The message defect is InvalidMultipartContentTransferEncodingDefect() This is caused by the presence of a Content-Transfer-Encoding: header in the headers of the multipart/signed part. This has been observed with macOS 12.0.1, Mail.app Version 15.0 (3693.20.0.1.32), and GPG Mail 6.0. We don't know if this applies to all PGP signed mail from Apple Mail 15.0 (3693.20.0.1.32) or only mail signed by GPG Mail 6.0.

The issue affects more than Mailman. In my case Thunderbird won't display the message body of such messages.

I have reported this to Apple, but have gotten no response so far.