ns1.dyndns.org has no MX records.
Question and response
Question
dig ns1.dyndns.org. MX
Answer
The response has no answer records.
Authority
dyndns.org. 600 SOA ns1.dyndns.org. hostmaster.dyndns.org. 2397923317 600 300 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0