[selowitch]

I have a question about the routing of e-mail, specifically conflicts between MX Records on two or more servers. Is this the proper forum for that, or does this belong elsewhere?

[ghporter]

I'm going to tentatively say that it belongs here, subject to someone smarter about email routing than I am telling me otherwise. Email, after all, is a network function.

Aside from that, I don't have a clue.

[selowitch]

That's what I thought. OK, so:
What happens if you have two servers each of which has a MX record for your domain that conflicts with the other? Which one takes precedence?

[larkost]

Which domain is run on the server that provides the authoritative DNS records. That is your answer. This is just like having a bad DNS entry on a non-authoritative server: the bad data will only propagate to clients that look to that server as a caching server.

[selowitch]

What makes a particular server authoritative and not others?

[ink]

There is a priority in the MX record. Here's a snippet from some of my domain tables:

Code:
foo.com      IN      MX      100     smtp.foo.com.
foo.com      IN      MX      200     smtp2.foo.com.
foo.com      IN      MX      300     smtp3.foo.com.

And, assuming that this is authoritatvie, a remote SMTP server should attempt to send mail to the lowest number first (smtp.foo.com), and work its way up. A lot of spam software does the opposite, because people are more likely to leave their backup SMTP servers unprotected. Also note that you must use domain names in the MX records, it is against the RFC to place IP addresses in there. Authority is derived from the DNS reseller that you use (buydomains.com, internic, etc.)