UNIX hosts and MX "best practice"

[Jim Reid]

>>>>> "Barry" == Barry Margolin <barmar at bbnplanet.com> writes:


    Barry> In article <23058.949106728 at gromit.rfc1035.com>, Jim Reid
    Barry> <jim at rfc1035.com> wrote:
    >> A bigger issue is the impact on the mail delivery and queues
    >> when mail is sent to hostnames that don't have MX
    >> records. Suppose that mail is sent to user at foo.example.com and
    >> there's no MX for foo.example.com.  The A record is looked up
    >> and the mail system will try to connect to port 25 on
    >> foo.example.com and speak SMTP. If foo.example.com doesn't have
    >> an SMTP listener, that connection will not succeed. The mail
    >> will get queued and sendmail (or whatever) will keep trying to
    >> deliver it for a few days or so before giving up. The mail
    >> system can't tell the difference between a remote system that's
    >> temporarily switched off its SMTP listener and one that *never*
    >> has such a thing. So the mail system's queues get cluttered
    >> with undeliverable mail and the postmaster gets a
    >> headache. Meanwhile the user is unhappy because their mail
    >> hasn't been received. Maybe the user was wrong to send mail to
    >> foo.example.com when it didn't have an SMTP listener. But if
    >> this host had an MX record, its mail could be delivered
    >> somewhere, even if it was only to some mail system that bounced
    >> the message because the email address was wrong.

    Barry> I assumed we were only discussing whether a host should
    Barry> have an MX record pointing to itself, versus just depending
    Barry> on the A record.

IIRC, the original question was "Should my hosts have MX records or not?
What's the best practice?"

    Barry> If its mail is supposed to be delivered
    Barry> somewhere else, it's intuitively obvious that it needs an
    Barry> MX record to get it there.  Why would you have people send
    Barry> mail to user at foo.example.com if it doesn't run a mail
    Barry> server and there's no MX record redirecting its mail?

Because users and software can do stupid things, like confuse a
hostname with an email address.