DKIM signature
Authentication & Alignment · Critical priority · hard-fail gate
What it is
DKIM cryptographically signs your mail so receivers can verify it was not altered and really came from your domain. Survives forwarding.
How to fix it
Enable DKIM signing with a >=2048-bit key (SHA-256) and publish the public key at selector._domainkey.yourdomain.
This is a hard-fail gate. If it fails, Gmail / Yahoo / Outlook may junk or reject your mail regardless of everything else — so fix it first.
Check your email
See how your real email scores on this and every other deliverability factor.