I have a few companies that I support and I would like to have all of them running off of one zimbra server. I have a few questions if anyone has been in this situation before:

What should I do about usernames? If I have multiple companies with multiple domains, but there are duplicate usernames among the orgs. For example, is I have TestUser@test1.com and TestUser@test2.com and they are different users, can I make the same username? If I can, how will they login to webmail? If I can't, I'll have to use something like TestUser.test1.com for the username and define an alias correct? Less than ideal...

Is the GAL limited to only the same domain or everyone?

Is there a way to define an admin for an individual domain so they can admin their own company?

I'm going through the documentation and testing as fast as I can, but I can't seem to get answers to these. Thanks in advance.