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unixdnsmx-recorddig

question about UNIX dig output

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?

Solution

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