mx3.pur3.net has no CNAME records.
Question and response
Question
dig mx3.pur3.net. NS
Answer
The response has no answer records.
Authority
pur3.net. 3182 SOA ns0.dnssub.com. hostmaster.pure360.com. 2025102201 10800 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0