Same username and password pair on more than one domain.

[admin]

The reason for this is that Ability Mail Server permits users to login into a service using just the user and the password (with no mention of the domain). If the same username and password pair existed on another domain, the mail server would have no way to know which was the correct account being logged into. However, you can configure the mail server to only allow login with the full email address, which will then allow the same username and password pairs to exist multiple times. This option can be found in the General settings under the Advanced tab.