SPF, DKIM, DMARC, sending reputation, and list hygiene. Fix deliverability issues before they tank your campaigns.
Email Authentication: SPF, DKIM, DMARC
These three protocols prove to inbox providers that your emails are legitimate. SPF (Sender Policy Framework) tells receiving servers which IPs are authorized to send email on your behalf. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to verify the email wasn’t altered in transit. DMARC (Domain-based Message Authentication) ties SPF and DKIM together and tells servers what to do with emails that fail authentication. All three are required for good deliverability.
Sending Reputation
Every sender has a reputation score based on bounce rates, spam complaints, engagement rates, and sending volume consistency. A poor reputation means your emails go to spam — even if the content is perfect. Check your reputation using Google Postmaster Tools and Sender Score. If your reputation is damaged, reduce sending volume, clean your list aggressively, and slowly warm the domain back up over 4–8 weeks.
List Hygiene: Clean Your Lists
Remove hard bounces immediately — they’re invalid addresses that hurt your reputation with every send. Suppress soft bounces after 3 consecutive failures. Remove subscribers who haven’t opened or clicked in 90 days (send a re-engagement campaign first). Never purchase email lists — they’re full of spam traps and will destroy your sender reputation overnight.
Content That Triggers Spam Filters
Avoid all-caps subject lines, excessive exclamation marks, and words like “free,” “guaranteed,” or “act now” in subject lines. Keep your image-to-text ratio balanced (don’t send image-only emails). Include a plain-text version alongside HTML. Always include a visible unsubscribe link and your physical mailing address — this is legally required by CAN-SPAM and GDPR.
Monitoring and Troubleshooting
Track deliverability metrics after every send: delivery rate (should be 95%+), open rate, bounce rate, and spam complaint rate (should be under 0.1%). If you see a sudden drop in open rates, check Google Postmaster Tools for reputation changes. Test your emails with tools like Mail Tester before sending to catch issues. And always send a test to yourself first.
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