Why your emails go to spam: 8 causes, in order of likelihood
"Our emails are going to spam" is the complaint; the cause is almost always one of eight things, and they're checkable in order. The first three are authentication problems you can find in ten minutes with free tools — and they're the culprit more often than content, volume, and blacklists combined.
Updated July 13, 2026
1. Missing or failing authentication (SPF/DKIM)
The most common cause by far since Gmail and Yahoo made authentication mandatory in 2024. If SPF or DKIM is missing, broken, or misaligned, filters downgrade you regardless of content. Check in two minutes: SPF checker, DKIM checker, then confirm end-to-end with the inbox test.
2. No DMARC record
A missing DMARC record is now a direct ranking signal at major providers — bulk senders are required to have one, and everyone else is treated better with one. v=DMARC1; p=none; rua=... costs nothing and starts the reporting that finds other problems. Setup guide here.
3. Your ESP authenticates as itself, not as you
Mail "from you" that authenticates as mail.some-esp.com passes technically but doesn't build your domain's reputation and fails DMARC alignment. Turn on custom-domain authentication in the ESP — our per-provider guides cover the exact records for each major service.
4. Spam-complaint rate above threshold
Gmail's line is 0.3% — above it, everything you send gets filtered aggressively. Complaints come from sending to people who don't remember opting in, or making unsubscribe harder than the spam button. One-click unsubscribe (List-Unsubscribe headers) is required for bulk mail now, and it's also self-defense: an easy unsubscribe is a complaint that didn't happen.
5. Sudden volume changes
Reputation systems model your normal. A domain that sends 50/day and suddenly sends 50,000 looks like a compromised account. Ramp new campaigns and new domains gradually — this is the entire logic behind "warming up" a domain or IP.
6. List quality: bounces and spam traps
High hard-bounce rates and hits on spam-trap addresses (recycled dead mailboxes) mark a list as purchased or stale. Remove hard bounces immediately, re-permission or drop addresses that haven't engaged in a year, and never buy lists.
7. Blacklisted sending IP or domain
Less common than people assume — it's usually the consequence of #4–6, not an independent cause. Check with the blacklist checker; if you're listed, fix the underlying practice first or you'll be relisted within weeks of delisting.
8. Content — the smallest factor, checked first by everyone
"Spammy words" matter far less than folklore says. Modern filters weigh sender reputation and authentication overwhelmingly more than whether you wrote "free." The content signals that do hurt: link-shortener URLs, mismatched link text vs destination, image-only emails, and sloppy HTML. If your authentication is clean and complaints are low, content is rarely what's sinking you.