mail.smtpeter.com has no CNAME records.
Question and response
Question
dig mail.smtpeter.com. NS
Answer
The response has no answer records.
Authority
smtpeter.com. 46 SOA dns1.proxi.nl. hostmaster.copernica.com. 1771944745 14400 1800 86400 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0