Luke Le on 10 Apr, 2018 12:43 AM
that was probably more luck than anything else.
GPGMail currently has only minimal highly experimental support for PGP data in winmail.dat files built-in. It also depends on what macOS version you are using GPGMail on. For example on macOS High Sierra, it will not try to handle winmail.dat at all if Letter Opener is installed, since we have yet to find a better way for the two plugins to co-exist on High Sierra.
We only added some support for winmail.dat/TNEF in the first place, because for some reason Microsoft Exchange Server, sometimes decides to pack an entire PGP/MIME message into a winmail.dat file. If you have such winmail.dat and you could share them for testing/debugging purposes, that would be interesting.
Generally for winmail.dat I recommend using Letter Opener. Full disclosure, the developer is a good friend of mine hence I know all the hassles he has to deal with when it comes to winmail.dat/TNEF