smtp.slcgov.com has no CNAME records.
Question and response
Question
dig smtp.slcgov.com. NS
Answer
The response has no answer records.
Authority
slcgov.com. 300 SOA authns2.qwest.net. abuse.centurylinkservices.net. 2260226000 10800 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0