MX record Question

Mark.Andrews at nominum.com Mark.Andrews at nominum.com
Thu Aug 9 21:51:38 UTC 2001


> > The question is how does this work?
> > 
> > MX 10 mail01.domain.com
> > MX 10 mail02.domain.com
> > 
> > 
> > If for example this in theory will round robin, what would happen if
> > mail01
> > were to go down, would mail02 be the next on the list even after being
> > resolved?  My email admin wanted to know how this would work.  We think
> > that
> > it should go to the next one in line, this of course depending on the MTA.
> > Could someone shed some light.
> > 
> > Thanks,
> > 
> > Mark
> > 
> > 
> When BIND returns a response to an MX query for this domain name, it will
> return the two entries ordered in round-robin fashion. So if mail01 was
> listed before mail02 in the response, the remote mailserver would first
> attempt to contact mail01, and then after a minute the TCP connection to
> port 25 (SMTP server) would fail, so the remote server would then try mail02
> and the mail would go through.
> 
> Steve

	It shouldn't matter about the order of the returned records as
	the MTA is require to randomise the order it selects from equal
	preference MX targets.

	Mark
--
Mark Andrews, Nominum Inc.
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at nominum.com


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