mail.3uu.org has no MX records.
Question and response
Question
dig mail.3uu.org. MX
Answer
The response has no answer records.
Authority
3uu.org. 180 SOA rc78.3uu.net. hostmaster.3uu.net. 20251211 10800 1800 604800 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0