allowed user gorups
UTM Authentication process in allowed User / Groups for Authenticated Relay
The UTM attempts to first authenticate the users to itself with AD before deciding whether or not users are listed in order to block or allow users/ groups the ability to relay emails through the UTM, when users have been added into the allowed users/group under allowed authentication Relaying in SMTP Global settings.
A preferred option would be to first check if users are listed first before attempting to go through authentication process with AD.
This allows for better performance as the UTM will go through authentication process only if user/ groups are listed in Allowed Users/groups