mail.fp-sign.com has no MX records.
Question and response
Question
dig mail.fp-sign.com. MX
Answer
The response has no answer records.
Authority
fp-sign.com. 600 SOA pns01.dcsix.net. hostmaster.dcsix.net. 2026022301 14400 3600 604800 600
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0