Limitation of Mail-Domains
i think, it make no sense, that a user can add a new email-domain other than the site-domains, the user "owns". For example: a user has: dom1.com dom2.com dom3.com
so it make no sense, that he can add a new email-domain called yxz.org.
i think even better is a drop-down box showing the site-domains he owns to select one of then.