MX Record Theories

gb10hkzo-nanog at yahoo.co.uk gb10hkzo-nanog at yahoo.co.uk
Tue May 26 13:03:59 CDT 2009


Hello all,

First, I hope this is not off-topic for NANOG, please be gentle with me as this is my first post.

I
would be most interested to hear NANOG theories on the variety of MX
record practices out there, namely, how come there seem to be so many
ways employed to achieve the same goal ?  Do you have experience in
more than one of these methods and which do you favour ?

To illustrate my question :

(1)
If you query the MX records for, Hotmail or AOL you will receive 4
equal weight MX records, each of the MX records having a round-robin
set of IPs.
e.g.
hotmail.com.        2706    IN    MX    5 mx4.hotmail.com.
hotmail.com.        2706    IN    MX    5 mx1.hotmail.com.
hotmail.com.        2706    IN    MX    5 mx2.hotmail.com.
hotmail.com.        2706    IN    MX    5 mx3.hotmail.com.
-and-
mx3.hotmail.com.    1926    IN    A    65.xxxxxxx
mx3.hotmail.com.    1926    IN    A    65.xxxxxxx
mx3.hotmail.com.    1926    IN    A    65.xxxxxxx
etc.etc.

(2)
Alternatively, some people, particularly the ones that use hosted
filtering, tend to have one MX record, which as multiple round robin
IPs.
e.g.
microsoft.com.        780    IN    MX    10 mail.global.frontbridge.com.
-and-
mail.global.frontbridge.com. 1728 IN    A    65.xxxxxxx
mail.global.frontbridge.com. 1728 IN    A    207.xxxxxxx
etc. etc.

(3) And others simply have a more traditional setup using multiple MX records and only one IP per MX record with no round robin
apple.com.        931    IN    MX    10 mail-in14.apple.com.
apple.com.        931    IN    MX    20 mail-in3.apple.com.
apple.com.        931    IN    MX    20 eg-mail-in2.apple.com.
etc.etc.


So
what's the big deal ?  Please note I'm not asking which is "better" ...
I am just curious and interested to hear your professional opinions and
experiences.

Personally, I favour the simple option 3, multiple MX records.

Thanks y'all.


      




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