im answering in this thread, because its reladet to the send-as Feature:
If a user replys from a mapped store from another the sender is the “userPrincipalName” not the e-mail-address from this user.
the user has another mail-domain we host in our ad. lets call it "domain1"
our main domain is “domain”
someone sends user2@domain1 a mail.
user has user2’s store mapped via koe
user replys or forward this mail from the mapped store
the recipient from the replyed or forwared message gets the mail from username@domain (like userPrinipalName in ad) - not even “domain1”
remember, the mails in our company are all like “surname.name@domain” or “surname.name@domain1” - this mail comes from “username@domain”
kopano-admin --details <username> gives as e-mail the right mail-address - same applys to user2
so still the same problem like my first post here