Emails go to spam when mailbox providers distrust the sender or the message. The most common causes are failed authentication, a poor sending reputation, a list with invalid or unengaged addresses, sudden volume spikes and spam-like content. You can diagnose most of them in an afternoon.
1. Authentication fails
If SPF, DKIM or DMARC fail, providers cannot confirm you are who you say you are. Open a sent message with Show original in Gmail and read the results. Fix with the authentication guide.
2. Your sender reputation is poor
Past complaints, bounces and spam-trap hits follow your domain and IP. Check Postmaster Tools and read how reputation is built and repaired.
3. The list is dirty
Mailing invalid, old or purchased addresses produces bounces and spam-trap hits. Clean it using email list hygiene and bounce rate guidance.
4. Recipients mark your mail as spam
Complaints are the strongest negative signal. They rise when people did not clearly agree to receive your mail, when frequency exceeds what you promised, or when unsubscribing is hard. Add one-click unsubscribe.
5. Volume jumped suddenly
A new domain or IP that sends a large campaign on day one looks like abuse. Ramp up with a warm-up schedule.
6. You are on a blocklist
Check your IP and domain on public lookups. See how to get delisted.
7. The content looks suspicious
Misleading subject lines, a single large image with no text, link shorteners, mismatched link domains and broken HTML all raise filters. Send a plain-text part and keep links on your own domain.
8. Infrastructure is incomplete
Missing reverse DNS, no TLS or a shared IP with a bad neighbor can drag results down. Read dedicated vs shared IP.
9. Low engagement
If few people open, click or reply, providers learn that your mail is unwanted and file it away. Segment by engagement and mail active contacts first.
Once you have the likely cause, run a deliverability test to confirm, then work through the improvement checklist.
Frequently asked questions
Why does my email go to spam in Gmail but not elsewhere?
Each provider keeps its own reputation data. Gmail may have more negative signals about your domain than Outlook does. Check Postmaster Tools for Gmail-specific data.
Can the words I use cause a spam placement?
Single words rarely decide it. Patterns such as deceptive subject lines and aggressive formatting matter more than a list of banned words.
Will asking recipients to add me to contacts help?
It can help for individual recipients, but it does not fix list, authentication or reputation problems.
How do I check why a specific email went to spam?
In Gmail, a spam notice sometimes explains why. Otherwise check authentication in the original message headers.