sfo4.bitnames.com has no MX records.
Question and response
Question
dig sfo4.bitnames.com. MX
Answer
The response has no answer records.
Authority
bitnames.com. 1200 SOA ns1.us.bitnames.com. dnsoper.bitnames.com. 2026021003 7200 3600 3628800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0