bunny01.rabbitmail.io has no MX records.
Question and response
Question
dig bunny01.rabbitmail.io. MX
Answer
The response has no answer records.
Authority
rabbitmail.io. 1800 SOA aria.ns.cloudflare.com. dns.cloudflare.com. 2397824756 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0