s2._domainkey.dbk.dk has no MX records.
Question and response
Question
dig s2.domainkey.u21117928.wl179.sendgrid.net. MX
Answer
The response has no answer records.
Authority
wl179.sendgrid.net. 1800 SOA aisha.ns.cloudflare.com. dns.cloudflare.com. 2397749610 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0