mail1.ip.metafour.com has no CNAME records.
Question and response
Question
dig mail1.ip.metafour.com. NS
Answer
The response has no answer records.
Authority
metafour.com. 354 SOA ns-1778.awsdns-30.co.uk. awsdns-hostmaster.amazon.com. 2014092501 7200 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0