ns3.sectigoweb.com has no MX records.
Question and response
Question
dig ns3.sectigoweb.com. MX
Answer
The response has no answer records.
Authority
sectigoweb.com. 3600 SOA ns1.sectigoweb.com. admin.sectigo.com. 1604434230 86400 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0