Question : POP3 Username with Exchange 2003 and Outlook 2003

Here is the scenario:
I have 300 clients currently using a POP3 server somewhere out on the internet.  They log into that mail server with [email protected].  We have installed an Exchange 2003 server.  We are changing the mail record tonight to point to our Exchange server.  So clients are going to be coming into our mail server for pop3 as of some time tonight/over the weekend.  

The problem:
The Exchange server does not take [email protected] when you try and make a pop3 connection to the server.  It works if you just use username.  Is there a way to make the Exchange server accept [email protected] for the email address's

Very Urgent, Mucho Importante

Thanks

Answer : POP3 Username with Exchange 2003 and Outlook 2003

I don´t see any problem to authenticate with upn([email protected]).
Please verify that [email protected] is the User Principal Name (upn and email address can be diferent).
Please try to use:  domain\user and tell us if it works.
Try to connect via telnet. On a command prompt from a client computer type:
telnet ipaddress 110
user [email protected]   (use upn, not email address)
pass yourpassword
list

MG