# The email glossary

> Plain-English definitions of the email alphabet soup: DKIM, SPF, DMARC, VERP, FBL, BIMI, warmup, suppression, and more — each with why it matters in practice.

Canonical: https://emailfast.dev/glossary

## Authentication & standards

- [DKIM](/glossary/dkim) — cryptographic signatures on your email
- [SPF](/glossary/spf) — which servers may send for your domain
- [DMARC](/glossary/dmarc) — the policy tying DKIM and SPF together
- [Email authentication](/glossary/email-authentication) — the three above, as a system
- [MTA-STS](/glossary/mta-sts) — enforcing TLS between mail servers
- [TLS-RPT](/glossary/tls-rpt) — reports on TLS delivery failures
- [BIMI](/glossary/bimi) — your logo next to your email in the inbox
- [List-Unsubscribe](/glossary/list-unsubscribe) — the one-click unsubscribe header
- [SMTP ports](/glossary/smtp-ports) — 25, 465, 587, and what each is for

## Deliverability mechanics

- [IP warmup](/glossary/ip-warmup) — earning trust for a new sending address
- [Dedicated IP](/glossary/dedicated-ip) — your own reputation, for better or worse
- [Bounce](/glossary/bounce) — hard, soft, and block, and why the difference matters
- [Suppression list](/glossary/suppression-list) — the do-not-send list that protects you
- [Spam complaint](/glossary/spam-complaint) — what happens when someone hits "report spam"
- [Feedback loop (FBL)](/glossary/fbl) — how complaints get back to senders
- [VERP](/glossary/verp) — how bounces are matched to the exact message
- [Seed testing](/glossary/seed-testing) — checking where your email actually lands

## The ecosystem

- [Transactional email](/glossary/transactional-email) — receipts, resets, and the mail that must arrive
- [Double opt-in](/glossary/double-opt-in) — consent you can prove
- [ESP](/glossary/esp) — email service providers, and who actually runs the servers