[nzlug] Understanding email DNS

[Robin Sheat]

On Thursday 05 October 2006 22:55, Michael Adams wrote:
> I was under the impression that the email for these domains had to
> go through e-Xperts mailserver. Yet one of the other regions tells me
> that their northern.foo.org.nz emails come direct to their server.
It does whatever it's been told to do, basically. 

When an email it to be delivered, the server looks up the hostname (e.g. 
eastcoast.foo.org.nz), finds the MX (Mail eXchange) record (e.g. 
mail.foo.org.nz) and sends the mail to that. If you added another subdomain 
(e.g. northern.foo.org.nz) and set the MX record to something else (e.g. 
kallisti.hopto.org), then all the mail @northern.foo.org.nz would go via my 
mail server (and bounce, but that's beside the point:)

To find out the MX records, do this:
$ host -t MX kallisti.net.nz
kallisti.net.nz mail is handled by 15 mail2.umbra.net.nz.
kallisti.net.nz mail is handled by 5 kallisti.hopto.org.
kallisti.net.nz mail is handled by 10 smtp.umbra.net.nz.

The numbers are the priority, lowest to highest, specifying the order the 
servers get tried in. If you compare the results of that command on 
eastcoast.foo.org.nz and northern.foo.org.nz, I expect you'll get a different 
result. Also note that the MX record is just a line in a file somewhere, so 
it can be changed to point whereever you like, typically at the most 
convenient mailserver, and some backups.

HTH,
-- 
Robin <robin at kallisti.net.nz> JabberID: <eythian at jabber.kallisti.net.nz>

Hostes alienigeni me abduxerunt. Qui annus est?

PGP Key 0xA99CEB6D = 5957 6D23 8B16 EFAB FEF8  7175 14D3 6485 A99C EB6D
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