DNS checks run from our server in Düsseldorf. No test emails are sent. STARTTLS optionally checks up to two public mail targets.
MX describes mail reception. SPF publishes permitted sending sources. DMARC describes policies for messages whose author domain is not validated through aligned SPF or DKIM. These settings serve different purposes.
DKIM checks the public key at the supplied selector, not a message signature. STARTTLS optionally checks connections to MX targets on port 25. MTA-STS, DANE, actual email sending and full deliverability are outside this check’s scope.