as per subject, if I send an email with Evolution or Apple Mail via O365 (both accounts configured with Exchange Web Services, IMAP/SMTP or POP/SMTP have not been tested), GpgOL with Outlook 2013 and 2016 cannot decrypt it.
If I send the same email using Outlook 2013 or 2016 using the same O365 account, GpgOL decrypts it properly.
I have done some debugging and I can confirm O365 is involved, using another email provider (we recently moved to O365), the problem did not occur.
Debugging this issue, I found that all emails received via O365 have in headers:
Content-Type: application/ms-tnef; name="winmail.dat" Content-Transfer-Encoding: binary
Emails sent from Outlook have a "gpgolXXX.dat" attachment, that is properly read and decrypted by GpgOL, while emails sent from Evolution and Apple Mail have two attachments, one text file with PGP MIME Version (Version: 1) and one with encrypted PGP message.
In the attached debug log, you can see starting at 15:23:06 that email message Content-Type is set to "application/ms-tnef", but GpgOL fails to parse message.
Last but not least, both Evolution and Apple Mail can decrypt those messages correctly.
I can do further testing and debugging if necessary, just let me know.