fallback.spamfilterserver.com has no MX records.
Question and response
Question
dig fallback.spamfilterserver.com. MX
Answer
The response has no answer records.
Authority
spamfilterserver.com. 3600 SOA ns1.thednscompany.com. ns1.thednscompany.com. 2026012919 28800 7200 1209600 3600
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0