smtp.slcgov.com has no MX records.
Question and response
Question
dig smtp.slcgov.com. MX
Answer
The response has no answer records.
Authority
slcgov.com. 300 SOA authns1.qwest.net. abuse.centurylinkservices.net. 2260109000 10800 3600 604800 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0