When I create a new user in exchange, it asks me to provide the User Logon Name. There is a dropdown box that supposedly allows you to select a domain for the user's login. What is this referring to? How can I make it so that I can create users with different domains in their user logon name?
p.s. I am very aware of 'Accepted Domains' in Exchange allowing one user to have several email addresses in different domains. I am just curious how I can modify the user's Logon name specifically.
Best Answer
As already noted in the comments, the last part of the User logon name is not an email domain.
The logon name, or User Principal Name, is made up of a user part (usually the same as the users SamAccountName) and a UPN suffix.
UPN suffixes are defined in Active Directory at the forest level, and you can add new UPN suffixes pretty easily, given that you have an Enterprise Administrator account in the forest:
Even though it's not email domains, all UPN suffixes should adhere to regular DNS naming conventions.
A number of AD integrated middleware applications like Lync 2010/2013 can automatically add user principal names as SIP addresses, in which case you might want to add a UPN suffix matching the public SIP domain.
In Exchange however, recipient addresses are easily managed with Email Address Policies. Unless the local domain UPN suffix is causing problems, just leave it be :-)