EV 11 - IMAP Konfiguration (external)

Hello,

i have installed EV 11 in a Test enviroment to test the new IMAP-Access. The internal access works fine but we can't access from external.

Can someone explain me exactly the way of communication of an external IMAP access? Which things must be prepared on the Exchange, EV and AD to make this work? Is the reverse proxy a must have? Or are there other ways of communication?

best regards