I just open this ticket in order to improve VirtualMin usability.
Indeed, a few customers called me because they got an error message when they tried to deactivate the mail feature on one of their domain (virtual server). The error message they got was "Failed to modify server : A target server must have email enabled if any aliases do".
I quickly discovered the problem came from the fact they were trying to disable mail on a top virtual server who contained sub-server and aliases with mail enabled.
I don't know if it's a bug or not but to disable mail on a top virtual server with children having mail enabled, you first need to disable mail on those sub-server/aliases.
I thing the error message should be clarified in some way: - either explaining the mail feature can't be disabled because some sub-servers/aliases use it, - offer the ability to disable mail feature for top server and all sub-servers/aliases, - list the concerned aliases by the error message (it may help understand the problem).