Email Deliverability: How to Stay Out of the Spam Folder

You can do everything else right and still fail if your emails land in spam. Deliverability is invisible until it breaks — and by then you've lost readers who never knew you sent anything. Here's how to protect it.

Authenticate your domain first The single biggest deliverability lever is authentication: SPF, DKIM, and DMARC records on your sending domain. Since 2024, Gmail and Yahoo require bulk senders to have all three, or messages get throttled or bounced. Every platform — Substack, beehiiv, Kit — gives you DNS records to add. Do this before your first send, not after you notice a problem.

Send from your own domain, not a free inbox Never send a newsletter from an @gmail.com or @yahoo.com "from" address — DMARC policies at those providers will reject it. Use a domain you control, like news@yourbrand.com, so authentication can actually pass.

Keep your list clean Inactive subscribers who never open quietly poison your sender reputation. Run a re-engagement campaign to anyone who hasn't opened in 90 days, then remove those who still don't. A smaller list with a 40% open rate delivers better than a bloated one at 15%. Also purge hard bounces immediately and use double opt-in to keep bad addresses out from the start.

Engagement is the real ranking signal Inbox providers watch what readers do: opens, replies, and "not spam" rescues raise your reputation; deletes-without-opening and spam complaints tank it. Keep complaint rates under 0.1% (Gmail's threshold is 0.3%). The best deliverability tactic is writing emails people genuinely want — engagement is both the goal and the mechanism.

Warm up a new domain slowly If you're on a fresh sending domain, don't blast 50,000 emails on day one. Ramp volume gradually over a couple of weeks so providers learn you're a legitimate sender. Most managed platforms handle warming for you, but it matters if you run your own SMTP or tools like Amazon SES.

Watch the content triggers Spammy formatting still hurts: ALL CAPS subject lines, "FREE!!!", too many links, one giant image with no text, and misleading subject lines all raise flags. Maintain a healthy text-to-image ratio and always include a working unsubscribe link — hiding it drives complaints, which is far worse than a clean opt-out.

The takeaway Authenticate (SPF/DKIM/DMARC), send from your own domain, prune dead weight, and earn engagement. Check your setup with a free tool like Mail-Tester before a big send. Deliverability isn't luck — it's hygiene.