Hello to Smartermail team,
I am now setting up an domain using SmarterMail V15.
As almost one of the best Microsoft Exchange alternative groupware system, 'User Groups' feature
seems not only "used to give permissions to specific subsets of users on the domain to access shared resources." It also should be able to become an alias as an option, and then easily appear in GAL.
Also, User Group should be able to set as a subet or a member of other User Group. In this case, remove or move user between groups will be easier.