Fix guides
DKIM Setup and Fix Guides
DKIM fails when DNS doesn’t match what signs the mail. Jump to your ESP or the “signature failed” cheat sheet.
SendGrid DKIM
CNAME records for SendGrid domain authentication.
Google Workspace DKIM
Generate and publish Google DKIM keys.
Microsoft 365 DKIM
Enable and rotate selector1/selector2.
Key Length
Move from 1024-bit to 2048-bit keys.
Signature Failed
Debug body hash and header canonicalization.
DKIM Selectors
Choose and publish the right selector.
Key Rotation
Rotate DKIM without delivery gaps.
Subdomain DKIM
Signing from subdomains vs root domain.
How to use these guides
Step 1 Open the guide for your ESP or DKIM error pattern.
Step 2 Publish the selector TXT or CNAME records at your DNS host in full.
Step 3 Run DNS Preflight to confirm DKIM and alignment.