Gpg4win changes the document type symbol for signed or encrypted mails in Outlook, which is visual information enough. But signed mails also have the attachment clip symbol, though the GPG attachment is resolved when displaying the mail. So we can't see in the mail list, if there is a "real" non-GPG attachment in the mail or not. In fact, all my sent mail have the clip symbol now.
- 3.1.0 beta 38
I doubt that I will be able to fix this. The problem is that for Outlook we build the signed mail structure, which is a multipart MIME message. If you receive such a mail with a non crypto client you see the plain text and a pgp-signature attachment. That is why Outlook shows it as "attachment".
This might be fixable if we somehow handle the mail after it was sent again and mark the signature attachment as hidden. But this will be quite a bit work.
As a workaround (although I won't recommend it) you could select "Send OpenPGP Messages without attachments as PGP/Inline" in the gpgol options. This won't produce an attachment but people without an OpenPGP enabled client will see the
-----BEGIN PGP SIGNED MESSAGE----- .... stuff. So this is probably even more ugly.