$ dig +short gmail.com MX
20 alt2.gmail-smtp-in.l.google.com.
5 gmail-smtp-in.l.google.com.
40 alt4.gmail-smtp-in.l.google.com.
10 alt1.gmail-smtp-in.l.google.com.
30 alt3.gmail-smtp-in.l.google.com.


$ dig +short alt2.gmail-smtp-in.l.google.com.
64.233.168.26
$ dig +short gmail-smtp-in.l.google.com.
74.125.130.27
$ dig +short alt4.gmail-smtp-in.l.google.com.
173.194.219.26
$ dig +short alt1.gmail-smtp-in.l.google.com.
74.125.28.26
$ dig +short alt3.gmail-smtp-in.l.google.com.
74.125.201.27
$ dig -x +short 64.233.168.26


$ dig -x 64.233.168.26 +short
oj-in-f26.1e100.net.
$ dig -x 74.125.130.27 +short
sb-in-f27.1e100.net.
$ dig -x 173.194.219.26 +short
ya-in-f26.1e100.net.
$ dig -x 74.125.28.26 +short
pc-in-f26.1e100.net.
$ dig -x 74.125.201.27 +short
in-in-f27.1e100.net.