sf03.spamfilteringcloud.com has no CNAME records.
Question and response
Question
dig sf03.spamfilteringcloud.com. NS
Answer
The response has no answer records.
Authority
spamfilteringcloud.com. 3392 SOA ns.cyberlynk.net. dnsadmin.cyberlynk.net. 2014091001 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0