mail.siteground359.com has no CNAME records.
Question and response
Question
dig mail.siteground359.com. NS
Answer
The response has no answer records.
Authority
siteground359.com. 6716 SOA ns1.siteground359.com. mail.siteground359.com. 15 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0