A customer using Active Directory with Kerio Connect needed to change the email addresses for several users. He coukdn't simply use an alias as another piece of software needed to authenticate and send with these names.
He tried just changing the names in AD, but that removed the old addresses from view. Kerio Support suggested this:
Stop Kerio Connect Server.
Navigate to the store, and locate each user's folder in turn.
There will be a folder for the new username, and a folder for the old username.
Rename the new user folder to something along the lines of newADusername_error
Rename the old user folder to EXACTLY the new AD username.
Start Kerio Connect Server, and the software should hook up to the "old" folders.