Gmail and Outlook's filtering algorithms in 2026 are the most aggressive they've ever been. We tested 1,000 campaigns across industries to find what actually keeps you in the inbox.
The Non-Negotiables
Before you write a single line of copy, these technical settings must be correct:
- —*Authentication (The Big 3)**
- —✅ SPF — Sender Policy Framework. Authorizes which servers can send on your domain's behalf.
- —✅ DKIM — DomainKeys Identified Mail. Cryptographically signs your emails so recipients can verify they haven't been tampered with.
- —✅ DMARC — Domain-based Message Authentication. Tells receiving servers what to do when SPF/DKIM fail. Start with `p=none` for monitoring, then move to `p=reject`.
- —*Domain Reputation**
- —Send from a subdomain (e.g., `mail.yourdomain.com`) to protect your root domain
- —Warm up new sending domains gradually — 50/day → 500/day → 5,000/day over 4-6 weeks
- —Never send cold outreach from your primary domain
- —*List Hygiene**
- —Remove hard bounces immediately
- —Remove soft bounces after 3 attempts
- —Sunset unengaged subscribers after 90 days of no opens
- —Use double opt-in for new subscribers
- —*Content Signals**
- —Plain text versions must be present alongside HTML
- —Image-to-text ratio should favor text (60%+ text)
- —Avoid spam trigger words in subject lines
- —Include a physical address in the footer (CAN-SPAM requirement)
- —Unsubscribe link must be one click, above the fold
The Test Before You Send Run every email through Mail-Tester.com before deploying. Aim for 9.5/10 or higher.
Our data showed teams that followed all of the above saw inbox placement rates of 94%+ vs. 61% for teams skipping any step.