smtp.covad.com has no MX records.
Question and response
Question
dig smtp.covad.com. MX
Answer
The response has no answer records.
Authority
covad.com. 300 SOA ns1.gtt.net. dnsadmin.gtt.net. 2026021901 14400 600 2718281828 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0