以下のコマンドでメールの設定情報を調べることができる。
（gmailで試して見た。）
$ nslookup
> set type=MX
> gmail.com
# 以下出力結果
Server: xxx.xxx.xxx.xxx
Address: xxx.xxx.xxx.xxx#x
Non-authoritative answer:
gmail.com mail exchanger = 20 alt2.gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 30 alt3.gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 5 gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 10 alt1.gmail-smtp-in.l.google.com.
gmail.com mail exchanger = 40 alt4.gmail-smtp-in.l.google.com.
Authoritative answers can be found from:
gmail.com nameserver = ns3.google.com.
gmail.com nameserver = ns2.google.com.
gmail.com nameserver = ns4.google.com.
gmail.com nameserver = ns1.google.com.
ns2.google.com internet address = 216.239.34.10
ns1.google.com internet address = 216.239.32.10
ns3.google.com internet address = 216.239.36.10
ns4.google.com internet address = 216.239.38.10