mail.teredo.pl has no MX records.
Question and response
Question
dig mail.teredo.pl. MX
Answer
The response has no answer records.
Authority
teredo.pl. 3600 SOA webh.pro. tech.webh.pro. 2021031924 3600 3600 604800 86400
Additional
. 0 OPT ; payload 2800, xrcode 0, version 0, flags 0