_spf.mailersend.net has no MX records.
Question and response
Question
dig _spf.mailersend.net. MX
Answer
The response has no answer records.
Authority
mailersend.net. 1800 SOA andy.ns.cloudflare.com. dns.cloudflare.com. 2396979189 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0