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Using the unix dig command, I can get the following MX record:

$ dig +nocmd gmail.com MX +noall +answer

gmail.com.      1868    IN  MX  20 alt2.gmail-smtp-in.l.google.com.
gmail.com.      1868    IN  MX  40 alt4.gmail-smtp-in.l.google.com.
gmail.com.      1868    IN  MX  5 gmail-smtp-in.l.google.com.
gmail.com.      1868    IN  MX  10 alt1.gmail-smtp-in.l.google.com.
gmail.com.      1868    IN  MX  30 alt3.gmail-smtp-in.l.google.com.

My question is, what does the fifth column (20, 40, 5...) mean?

eykanal
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2 Answers2

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The numbers give the relative preference of the MX records. Lower values are more preferred. See RFC 1035

heijp06
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It's the "Priority" of the MX records, some people have two sets of MX records using the secondary MX records as a backup.

BLAKE
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    Hey, thanks for the answer. Not sure how you found this, but you should note that it was asked in 2009... I've kind of moved on from this project :) If you want to answer some of the more current questions, see the main [StackOverflow page](http://www.stackoverflow.com/). – eykanal Apr 11 '12 at 18:32