Our LISTSERV server is set to use our Exchange 5.5 SP4 server for sending messages. Worked great until we had some issues with viruses and spam. Now, LISTSERV will send messages to internal addresses fine, but addresses outside of our domain don't ever get delivered. There has to be a simple solution, but I can't find it. The SMTP_forward setting in LISTSERV is set to mail.ourdomain.com like it always has been. Exchange is set to accept relay from the LISTSERV server's private IP address, but nowhere else. I get no error messages. The only way we know that a message hasn't been delivered to the external addresses is when someone calls. Any ideas where to start?