pop3.cityofsergeantbluff.com has no MX records.
Question and response
Question
dig pop3.cityofsergeantbluff.com. MX
Answer
The response has no answer records.
Authority
cityofsergeantbluff.com. 3600 SOA ns1.longlines.com. postmaster.longlines.com. 721599679 7200 3600 1728000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0