Email Deliverability Checklist: Stop Landing in Spam

Email marketing only works if emails arrive. Deliverability—the ability to reach inboxes rather than spam folders—determines whether your campaigns have any effect at all.

Poor deliverability is often invisible. Your ESP reports emails as "delivered" when they're accepted by the receiving server, not when they reach inboxes. The difference between 90% inbox placement and 60% inbox placement might not show in your dashboard but has massive impact on results.

Understanding what affects deliverability helps you protect this critical metric.

Authentication fundamentals

Email authentication proves your emails come from you—not from spammers impersonating your domain. Three protocols work together.

DKIM (DomainKeys Identified Mail) adds cryptographic signatures to your emails. Receiving servers verify the signature to confirm the email wasn't altered in transit and actually came from your domain.

DMARC (Domain-based Message Authentication, Reporting & Conformance) tells receiving servers what to do when SPF or DKIM fails. A proper DMARC policy protects your domain reputation by rejecting unauthorized senders.

If you're not running all three correctly, you're starting at a disadvantage. Most ESPs handle this—but verify rather than assume. Improperly configured authentication is surprisingly common.

Sender reputation factors

Mailbox providers (Gmail, Microsoft, Yahoo) maintain reputation scores for sending domains and IP addresses. Poor reputation means spam folder placement regardless of content.

Engagement rates are the most important factor. High open rates, clicks, and replies signal that recipients want your email. Low engagement—especially combined with spam complaints—damages reputation.

Spam complaints carry heavy weight. Even 0.1% complaint rates can trigger filtering. Keeping complaints minimal requires clear expectation-setting and easy unsubscribes.

Bounce rates matter, especially hard bounces (invalid addresses). High bounce rates suggest poor list hygiene and trigger provider suspicion.

E-commerce brands often struggle with deliverability during peak seasons when sending volume increases dramatically—the inconsistency triggers additional scrutiny.

List hygiene practices

Your list is an asset that degrades over time. Addresses go bad, engagement wanes, and stale subscribers hurt deliverability.

Regular cleaning removes dead weight. Addresses that hard bounce should be removed immediately. Addresses with no engagement over 6-12 months should be sunset or re-confirmed.

Sunset flows give inactive subscribers a final chance. "We haven't heard from you—still interested?" One last engagement attempt before removal protects list quality while recovering some subscribers.

Double opt-in confirms intent. Requiring confirmation before adding subscribers ensures valid addresses and interested recipients. The slightly lower list growth is offset by dramatically better engagement rates.

Content and technical factors

Some content patterns trigger spam filters. Excessive caps, spam trigger words, image-only emails, and suspicious links all raise red flags.

Email size matters. Very large emails (over 100KB) load slowly and may be clipped. Keep emails focused and appropriately sized.

HTML quality affects rendering and deliverability. Broken HTML can trigger filters and looks unprofessional if it reaches inboxes.

Plain text alternatives ensure deliverability when HTML fails. Always include a plain text version of your emails.

Landing the inbox requires ongoing attention to authentication, reputation, list health, and content. It's infrastructure maintenance, not a one-time setup.

Building email marketing systems that perform means treating deliverability as foundational—not assuming it's handled until problems emerge.