ns1a.dub1.discourse.cloud has no MX records.
Question and response
Question
dig ns1a.dub1.discourse.cloud. MX
Answer
The response has no answer records.
Authority
dub1.discourse.cloud. 2560 SOA ns1.discourse.cloud. hostmaster.discourse.org. 1772567090 16384 2048 1048576 2560
Additional
The response has no additional records.