webmail.dynu.com has no CNAME records.
Question and response
Question
dig webmail.dynu.com. NS
Answer
The response has no answer records.
Authority
dynu.com. 2967 SOA ns1.dynu.com. administrator.dynu.com. 76176330 1800 300 86400 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0