bt.es has no MX records.
Question and response
Question
dig bt.es. MX
Answer
The response has no answer records.
Authority
bt.es. 600 SOA ns1.bticglobal.net. hostmaster.eu.bt.net. 2021050635 3600 1800 1814400 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0