s/mime still not workin in MS Exchange environment => NOT solved
Neither the GPG-Plugin nor the S/MIME Plugin work if you use an MS Exchange Server - so for my environment it is NOT solved. Support is involved since 12 months without any solution. Very poor performance.
This feature is NOT solved, if you use an exchange server with Airmail. Under this condition the plugin crases every time you try to send a message. Airmail support answered a year ago that they will fix it. Guys from Airmail - please prioritize encryption over unnecessary usability features!