We have upgraded some workstations from Windows NT to XP and no longer are able to send email from within the local network using MS Outlook. We were able to do so when on NT. The IP addresses are the same, as are the user id's and passwords. The user is able to POP in and retrieve their email, but get a relaying denied error (553) when they try to send to anyone whose email address is in a domain not on our server.
Samba is working just fine. This server is only acting as their web and email server.
The configuration of the server has not changed in any way.