mta124.3.donweb.com has no MX records.
Question and response
Question
dig mta124.3.donweb.com. MX
Answer
The response has no answer records.
Authority
donweb.com. 1800 SOA carol.ns.cloudflare.com. dns.cloudflare.com. 2396152988 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0