The Practical Email Deliverability Guide
Authentication, reputation, warmup, and list hygiene — the unglamorous work that decides if anyone sees your email.
The most beautiful, perfectly on-brand AI email is worthless in the spam folder. Deliverability is the part of email marketing nobody posts screenshots of, and it's the part that decides whether any of your work gets seen. Here's the practical version.
Authentication: do this first
Three records prove you're allowed to send as your domain. They are not optional in 2026 — major mailbox providers require them for bulk senders.
- SPF: lists the servers allowed to send for your domain.
- DKIM: cryptographically signs your mail so receivers can verify it wasn't tampered with.
- DMARC: tells receivers what to do with mail that fails SPF/DKIM, and gives you reporting. Start at p=none to monitor, then move to quarantine/reject.
Reputation is earned, slowly
Mailbox providers score your sending domain and IP based on how recipients react. Opens, replies, and "not spam" help; spam complaints, hard bounces, and spam-trap hits hurt. Reputation is sticky in both directions, so protect it.
Warmup
New domains and IPs have no reputation. Ramp volume gradually over weeks, starting with your most engaged subscribers, so providers learn you're a legitimate sender. Several platforms (Klaviyo, Resend, SendGrid) offer guided warmup and reputation monitoring.
List hygiene beats every other trick
- Only mail people who opted in. Bought lists are a fast track to blocklists.
- Use double opt-in where you can; validate addresses at signup (SendGrid and others offer validation APIs).
- Sunset unengaged subscribers. Mailing people who never open drags your whole reputation down.
- Make unsubscribing trivial. A hidden unsubscribe link generates spam complaints, which are far worse.
How AI helps — and where it doesn't
AI helps at the margins of deliverability: send-time optimization (Klaviyo's Smart Send Time, ActiveCampaign's predictive sending), reputation monitoring, and content checks that flag spammy patterns. But understand the boundary clearly: AI generation — writing and designing the email — does nothing for inbox placement. A great AI tool like Brew makes the email excellent; authentication, reputation, and hygiene get it delivered. You need both.
Frequently asked questions
Why are my emails going to spam?
Most often: missing or misconfigured authentication (SPF/DKIM/DMARC), poor list hygiene (unengaged or purchased contacts), a cold domain sent at high volume, or high spam-complaint rates from a buried unsubscribe.
Does AI improve deliverability?
Indirectly. AI helps with send-time optimization, reputation monitoring, and flagging spammy content. It does not affect inbox placement through generation — authentication, reputation, and list hygiene do that.