Initial situation:

In rare cases, the situation occurs that the recipient of signed emails with attachments has smime.p7m attachments instead of the original attachments.

This might also apply to GINA messages, as their included HTML attachment "securemail.html" with the actual email also is displayed as "smime.p7m" and therefore cannot be opened.

 

Finding:

Up to now, this behaviour has only been observed with recipients that use the combination of

•Google mailbox

•Outlook Version 16.55 for macOS in Classic Modus

 

Analysis of this behaviour is underway with the third party providers involved.