For example, some fo the "cpanel" hosts out tehir are hosting over 400 domains, lots of those domains will be using the e-mail address "webmaster@thatdomain.com" if you have 400 domains with the current state of ISPManager, you'll only be able to use each name once over the 400 domains. Lots of people are going to want to be able to use
admin@theirwebsite.com and if someone else has already used that name on their domain it's not going to be available for someone else.