Hey guys, I'm having a huge problem when it comes to attempting to send emails from our network and the POP3 users. This has been an ongoing problem that has peaked, and is basically shutting down the municipality's ability to send email outside. They can send emails back and forth inside, however outside just fails. When users attempt to send mail, they get the following error message: That is the error message, with some changes made to account for security. My co-worker and I are banking on that it has to do with the authentication being made by the users. The users are setup as INETORGUSERS so that they can use POP3 (they're on a different network than the Exchange server; 2 networks, 1 building). They set the POP3 to connect to the server, and that they have to authenticate before being able to send. But now for whatever reason we get that message as soon as we hit send / receive. I have verified that the firewalls on both sides aren't denying the connections. We've also confirmed that the new spam filter we've implemented (Barracuda) is not doing the outbound scanning and should not be interfering. So what's the problem? The only thing I can think of causing problems is that before we implemented the spam filter, we ran about 25 updates or so for the Exchange Server. Any ideas?