MX Records

[Igmar Palsenberg]

> > We don't have a backup mail server as of yet, so is both preferences
> > required that point to media.metzgers.com? (What is preference=0 used for?
> > Webhosting.com tells me that it is the timeout value and is required,
> > although as I do a lookup on other servers, it does not appear that many use
> > it.)
> 
> Geez. In all my days, I've never heard *that* one before! They are clueless.
> The preference value is just that: a *preference* value. Lower numbers
> represent more preferred targets. They _are_ correct, however, in saying that
> it is a required field. If you have only one server, just list one MX record,
> and the preference value doesn't matter (I usually set it to 0 just for
> readability). It looks goofy to have two MX records with the same target and
> different preference values...

Yeah.. I wonder if it confuses things.. Looking at the problems, it's
probably the NAT box causing the problems. 

> Tell the folks at webhosting.com to read RFC 1035 for an education on the
> meanings of the various fields in the "original" DNS record types, including
> MX. RFC 974 provides even more information about how MX records, in particular,
> should be used in practice. Ignore all references to "WKS" records; they are
> obsolete.
> 
> > Could that be causing a loop that is delaying the delivery of mail?

No. All MTA's bark loudly when they encounter a loop. 

> Nope, it shouldn't. As long as your mail server is available, the fact that you
> have 2 MX records with the same target shouldn't cause any "loop" at all, since
> the second MX record won't be used. Even if it is, it should be relatively
> harmless for remote mailservers to retry the same mail message to the same mail
> server. And your mail server wouldn't be using MX records to figure out whether
> or not to accept a piece of mail either: this is configured right into the mail
> server. So it wouldn't cause a loop. A loop probably wouldn't generate those
> error messages, either. With sendmail, for instance, a loop usually dies with
> "Too many hops" or "hop count exceeded".
> 
> I'd be scrutinizing your NAT or your mail server instead of DNS.

Same thought.. The most probable cause is that the NAT box is dropping
connections. The easiest way is to increase the Sendmail loglevel, so that
it also logs the connections itself.

I had a major headache with a mailserver behind a Firewall-1 box. Same
errors, lots of connections getting droppen, but not all.

Putting the server on the other side 'fixed' the problem.

> - Kevin



	Igmar