workaround for "partially GPG signed, partially GPG encrypted" when encrypted message sent over Exchange EWS
Reporting this behavior for future users googling for this symptom.
Action
Send a GPG encrypted message over Exchange EWS with Evolution
Actual Behavior
Upon reception, the message shows as "partially GPG signed, partially GPG encrypted (Show parts not being secured)". This creates a sense of distrust for users.
Expected Behavior
The message shows as fully secure ("Security: GPG signed, GPG encrypted"), because it is.
Additional details
This is due to the MS Exchange EWS API changing the MIME structure. So it's an Exchange bug, which is basically almost impossible to fix. A client level workaround might help.
Evolution 3.52.0 Flathub