mail.bt-telekom.com.tr has no MX records.
Question and response
Question
dig mail.bt-telekom.com.tr. MX
Answer
The response has no answer records.
Authority
bt-telekom.com.tr. 7200 SOA dnx1.vodafone.net.tr. dnsadmin.bt-telekom.com.tr. 2019090917 86400 7200 3628800 7200
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0