ns3.attdns.com has no MX records.
Question and response
Question
dig ns3.attdns.com. MX
Answer
The response has no answer records.
Authority
attdns.com. 300 SOA ns0.attdns.com. eiss-dns.att.com. 2026011901 3600 1800 2592000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0