Using Outlook (32 bit) as part of O365 ProPlus. Version 1708 (build 8431.2107 Click to Run), connected to Exchange Online. Windows 10 64 bit.
Kleopatra v3.0.1-gpg4win-3.0.2, GpgOL v2.0.5
S/MIME support is not enabled, Send OpenPGP mails without attachments as PGP/Inline is enabled.
I can successfully send a signed email to an external recipient.
If I try and send an encrypted email, I get a bounce back from the Exchange Server, with the following message:
'550 5.6.0 M2MCVT.StorageError.Exception: ConversionFailedException, Content conversion: Invalid S/MIME encrypted message.; storage error in content conversion.