mx1.antispamgw.host has no CNAME records.
Question and response
Question
dig mx1.antispamgw.host. NS
Answer
The response has no answer records.
Authority
antispamgw.host. 337 SOA ns.aname.net. hostmaster.antispamgw.host. 1729669701 10800 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0