host command is used for dns lookup
root@server1 [~]# host -t mx gmail.com gmail.com mail is handled by 5 gmail-smtp-in.l.google.com. gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com. gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com. gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com. gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com. root@server1 [~]# host gmail.com gmail.com has address 74.125.113.18 gmail.com has address 74.125.113.83 gmail.com has address 74.125.113.17 gmail.com has address 74.125.113.19 gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com. gmail.com mail is handled by 5 gmail-smtp-in.l.google.com. gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com. gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com. gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com. root@server1 [~]#