I'm somewhat familiar with Linux and became pretty decent at installing and configuring packages in Ubuntu. One of the things I was able to do with my tinkering was set up a functioning imap and pop3 mail server using dovecot-postfix.

Now I'm experimenting with Slackware to get the feel of another distro, and I noticed that the mail server packages were already installed. On my client computer they can pick up that I have users configured and my mx record is working.

However it is failing to send mail saying that it is failing to relay the e-mail message and that the server responded 5.7.1 which was a problem that I was having in Ubuntu when first configuring the mail server. The fix was to edit the postfix.conf file and adding the localhost name of my server.

Does anybody know of the file that I need to edit to make it possible to relay my messages with both pop3 and imap.

Assuming you're using Sendmail, check here: http://www.sendmail.org/~ca/email/relayingdenied.html