mx3.bit.org has no MX records.
Question and response
Question
dig mx3.bit.org. MX
Answer
The response has no answer records.
Authority
bit.org. 28800 SOA ns1.rrpproxy.net. tech.rrpproxy.net. 2025105744 10800 3600 604800 28800
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0