After doing this I wanted to make damn sure that I hadn't inadvertantly created an open relay. I wasn't too concerned, since the box is setup to require SMTP authentication before allowing a user to send mail via the box, but complacency isn't something I can afford here. I tested this three ways:
- Attempted to send mail through the box using my test account, using Mail.app. The unauthenticated SMTP session was rejected, while the authenticated session worked.
- While logged into the box via SSH, I telnetted to relay-test.mail-abuse.org, which runs a script that attemtps to relay mail through the box. All attempts to do so failed.
- Ran SpamHelp.org's web-based test on the box's IP. It came up negative.
Now all we need to do is schedule a time to migrate them over. It looks like we'll be recyling the old box into a secondary mail server, to be located at their other office. I'll create a clone of the new box on the old one, with appropriate changes such as hostname, etc.