i try to explain:
we got three groups with their own websites and their own mail-accounts/domains.
group1 has @example1.com mail accounts and uses
http://mail.example1.com to login on webmail.
group2 has @exampe2.com mail accounts and has to use mail.example1.com to login on webmail as well. this is the problem. i want group2 to use mail.example2.com