I've tried to send GPG encrypted messages in Outlook 2010 with GpgOL 2.0.6.
OpenPGP w/o attachments not encrypted as PGP/inline option
- empty content displayed both in Inbox and Sent folder (with GpgOL enabled)
- empty content and "gpgolXXX.dat" as attachment (with GpgOL disabled)
It is possible to decrypt gpgolXXX.dat via GPA outside of Outlook (save attachment and open in GPA)
OpenPGP with attachments encrypted as PGP/inline option
PGP message is shown literally (-----BEGIN PGP MESSAGE----- .... -----END PGP MESSAGE-----), but no decryption (GpgOL icon flags "unsafe" message). Message marked as encrypted (lock icon) in Inbox folder. Message can be decrypted via GPA outside of Outlook (clipboard used to copy text).
See complete message "GPG 3 0 3 Inline HTML.msg"
This behavior is independent of GPG options for S/MIME support and Outlook options to convert RTF to plain text or HTML. But obviously, some Virus scanner and classification tools change e-mail content on exchange server.