Email Authentication

Authentication proves to inbox providers that you are who you claim to be. It is the foundation of deliverability. Without it, no amount of content or list quality will reliably get you to the inbox.

Related skills: deliverability/SKILL.md (overview), monitoring/SKILL.md (how to verify authentication is working in practice via Postmaster Tools)

The four layers, in order of implementation:

SPF   → Authorizes which servers can send on your behalf
DKIM  → Cryptographically signs your messages
DMARC → Tells inbox providers what to do when SPF/DKIM fail
BIMI  → Displays your brand logo in supporting inboxes