Why Your Emails Land in Spam: 7 Common Causes and How to Fix Them

Spam filters do not look at a single signal. They combine authentication results, sender reputation, recipient engagement and content into one decision. That means there is rarely one "magic fix" — but in practice, the same handful of problems causes most deliverability issues.

1. Missing or broken authentication

Without SPF, DKIM and DMARC, mailbox providers cannot verify that you are allowed to send as your domain. Unauthenticated mail is treated with suspicion, and major providers now reject much of it. A common subtle issue: a third-party tool (CRM, help desk, newsletter platform) sends as your domain but is not included in SPF and does not sign with DKIM.

2. Your IP or domain is on a blacklist

If your sending IP or domain appears on a widely used blocklist such as Spamhaus, many receiving servers will reject or junk your mail. Listings usually follow a spike in complaints, spam-trap hits or a compromised account. Check your status regularly — a listing can happen overnight.

3. Poor list hygiene

Old, purchased or scraped lists contain invalid addresses and spam traps. High bounce rates (above roughly 2%) and trap hits are strong negative signals. Use confirmed opt-in, validate addresses at signup and remove hard bounces immediately.

4. Low engagement

Mailbox providers watch how recipients react. If most people never open your emails, delete them unread or mark them as spam, future messages are more likely to be filtered. Segment by activity and stop mailing subscribers who have not engaged in months.

5. Hard-to-find unsubscribe

When unsubscribing is difficult, recipients click "Report spam" instead — and complaints are one of the most damaging signals. Add one-click unsubscribe headers and a clear link in the footer.

6. Sudden volume spikes

Sending a large campaign from a new domain or IP, or suddenly multiplying your usual volume, looks like spammer behaviour. Warm up new infrastructure gradually over several weeks and keep volume consistent.

7. Spammy content and formatting

• Link shorteners and links to domains with a bad reputation
• Image-only emails with little or no text
• Misleading subject lines or "Re:" / "Fwd:" tricks
• Mismatched From name, reply-to and link domains
• Broken HTML or missing plain-text alternative

Where to start

Fix the technical foundation first — authentication and blacklist status are binary and easy to verify. Run a check on your domain, apply the recommendations, then move on to list hygiene and engagement, which take longer to improve.