Web Access logins

[Buzzard2k2]

I am running NW6.5 and GW6.5 using WebAccess. I will refer to this as my post office.
We have another post office that we maintain system visibility with and can see each others address book etc. They are running GW7. I will refer to this as the remote post office.

The problem:

If my post office has a user named user1 and the remote post office also has a user named user1, then user1 cannot use my WebAccess.

Reality:
I have a user with an account here and in the remote post office using the same username. He has GW7 client on his PC which he uses to access the remote PO. He is trying to use WebAccess for my PO because GW6.5 and GW7 clients don't work on the same PC. The WebAccess denies his login because I am assuming it can't tell whether he wants to login as the GW6.5 user or the GW7 user. Is there a way to define your username@postoffice to get around this? Is there a way to limit my WebAccess to only accept users from my post office?

Thank you in advance.

Greg