How to improve email deliverability: the technical and content checklist
Deliverability problems are invisible until you notice your open rate dropped from 30% to 8%. By then, you've damaged your domain reputation — which takes months to recover.
Fix the technical and content issues that send your emails to spam before they reach the inbox.
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Resolution protocol
- 01
Technical setup: SPF, DKIM, DMARC
SPF: tells mail servers which IPs can send on behalf of your domain. DKIM: cryptographic signature that proves the email wasn't tampered with. DMARC: policy that tells servers what to do if SPF/DKIM fail (reject, quarantine, or monitor). Without all three, Gmail and Outlook will filter your emails by default. Verify at mail-tester.com — target score: 10/10.
- 02
List hygiene: the forgotten deliverability factor
Remove hard bounces immediately (invalid email addresses damage your sender score every time they're sent to). Remove soft bounces after 3 attempts. Suppress unengaged contacts (no opens in 6 months) from broadcast sends. Email lists naturally decay at 20–25% per year. Clean quarterly.
- 03
Content that avoids spam filters
Avoid: all-caps subject lines, excessive exclamation marks, spam trigger words ('FREE!!!', 'Act now'). Use: plain HTML with minimal images (heavy image emails trigger promotions tab). Text-to-image ratio: 80% text / 20% images. Test your emails at mail-tester.com and GlockApps before any major send.
FAQ
Why are my emails going to spam?
Most common causes in order: missing DMARC record, sending to unengaged subscribers, spam trigger words in subject, high bounce rate from dirty list, sudden volume spike (5 emails/month → 50,000 in one week). Start with mail-tester.com to identify your specific issues.