Build the Records That Stop Mail Being Sent as You DMARC
SPF, DKIM and DMARC decide whether the world trusts mail claiming to be from you. They are hand-written records where one slip lets a spoofer through. This builds them right and checks the ones you have.
Your domain
SPF — who may send your mail
DMARC — what to do with mail that fails
DKIM — sign your mail
security.txt — how to report a problem to you
Check a record you already publish
Paste an SPF, DMARC or security.txt record and it is read back for the faults that matter.