Why are my emails going to spam? 10 causes and how to fix them
The email has gone out, but at the recipient it ends up in the spam folder. Usually it's not a single word in the subject line but the technology behind it or your sending behavior. Here are the ten most common causes – and what you can do about each.
1. Missing or wrong authentication
Without SPF, DKIM and DMARC, mailbox providers can't verify that the email really comes from you. Gmail and Yahoo now explicitly require these records.
Solution: Create all three records and make sure that every service sending for you is included. The article SPF, DKIM and DMARC explained shows how.
2. The server IP is on a blocklist
Blocklists like Spamhaus collect IP addresses that sent spam. If your server IP is listed, many mailbox providers reject your emails. This particularly affects shared IPs at cheap web hosts, where another customer sent spam.
Solution: Find and fix the cause, such as a hacked account or an abused contact form. Then request removal on the list's website. With shared IPs, involve your provider or use a specialized sending service for newsletters.
3. No matching reverse DNS
Every IP has a reverse DNS record (PTR) that names a host – and this name should point back to the same IP. If it's missing or looks like a residential internet connection, your server looks like an infected home computer.
Solution: Have the PTR record set by the owner of the IP, usually in your hosting provider's control panel. It should point to the name your mail server uses to identify itself.
4. The sender doesn't match the sending service
You write as news@example.com, but your newsletter tool signs and sends with its own domain. For DMARC that's a failure, even if the tool itself works cleanly.
Solution: Authenticate your own domain in the newsletter tool, i.e. add the DKIM and return-path records it shows to your DNS.
5. New domain or new IP without reputation
Mailbox providers trust senders they know. A brand-new domain that immediately sends thousands of emails looks suspicious – even if everything is technically correct.
Solution: Start slowly (“warming up”): first to your most active recipients, then increase the volume over a few weeks. Send evenly instead of in large waves.
6. Too many recipients mark your emails as spam
Every click on “Report spam” hurts your reputation. Google names 0.3 % complaints as the upper limit; a good value is below 0.1 %.
Solution: Only send when recipients expect it. Make sender and subject clearly recognizable so nobody mistakes the email for a stranger's. Make unsubscribing easy to find – people who can unsubscribe mark emails as spam less often.
7. Old, purchased or poorly maintained address lists
Old lists contain addresses that no longer exist and sometimes so-called spam traps: addresses that only exist to identify spammers. In the EU, purchased lists are generally not permitted anyway.
Solution: Use double opt-in, remove undeliverable addresses immediately and weed out recipients who haven't opened anything for many months.
8. The content looks like advertising
Content filters look for typical patterns: emails consisting almost entirely of one large image, a missing plain-text version, lots of exclamation marks and capital letters, sensational subject lines or large attachments.
Solution: Write real text, use images as a complement with alt text, include a plain-text version and keep the HTML lean. Gmail clips emails above 102 KB of HTML – and then the unsubscribe link often disappears too.
9. Suspicious links
Links are checked just like the sender. Short links like bit.ly hide the destination and are popular with spammers. Links to domains with a bad reputation drag your email down too.
Solution: Link directly to your own domain. For click tracking, use your newsletter tool's tracking with your own tracking domain. Fix broken links.
10. No easy way to unsubscribe
For newsletters, Gmail, Yahoo and Outlook.com require one-click unsubscribe right in the mailbox. Without it, the email is rated worse – and annoyed recipients use the spam button instead.
Solution: Set the List-Unsubscribe and List-Unsubscribe-Post headers or enable them in your newsletter tool, plus a visible unsubscribe link in the body. More on this in the article about the rules of Gmail, Yahoo and Outlook.
What a test can show – and what it can't
Causes 1 to 4 and 8 to 10 can be checked on a single email. That's exactly what the test on the home page does: SPF, DKIM, DMARC, blocklists, reverse DNS, content, links and unsubscribe headers, with concrete advice on how to fix them.
Causes 5 to 7, on the other hand, depend on your sending behavior. Only the mailbox provider sees that. For Gmail, the free Google Postmaster Tools show your reputation and your complaint rate.