mail.turbo-smtp.com has no MX records.
Question and response
Question
dig mail.turbo-smtp.com. MX
Answer
The response has no answer records.
Authority
turbo-smtp.com. 900 SOA ns1.softlayer.com. support.softlayer.com. 2026020301 7200 600 1728000 900
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0