Glossary

DKIM — DomainKeys Identified Mail Explained

DKIM adds a crypto signature to each outbound message. Receivers pull your public key from DNS and verify the body and headers weren’t tampered with. No signature or bad key = “DKIM fail” in headers.

How DKIM Works

Your MTA signs with a private key. DNS holds the public key at something like selector._domainkey.yourdomain.com. Match = pass.

DKIM Key Strength

Use 2048-bit keys today. 1024-bit is legacy — some receivers already side-eye it.

DKIM Selectors

The selector is just a name for which key you’re using — google, s1, selector1, etc. Different vendors use different ones.

How to Check Your DKIM

DNS Preflight probes common selectors and shows key size. Paste your domain and go.