pl4304.mex1.stableserver.net has no MX records.
Question and response
Question
dig pl4304.mex1.stableserver.net. MX
Answer
The response has no answer records.
Authority
stableserver.net. 3600 SOA ns1.stableserver.net. postmaster.stableserver.net. 2026022410 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0