When email lands in spam, the cause is usually not one "bad word" in the message. Mailbox providers such as Gmail, Outlook and Yahoo look at who is sending (authentication and reputation), how it is sent (server setup) and how recipients react. Work through the causes below in order — the first ones are the most common and the easiest to fix.
1. Missing or broken SPF
SPF is a DNS TXT record listing the servers allowed to send email for your domain. If the service you send through (Google Workspace, Microsoft 365, your newsletter tool, your website) is not in it, receivers treat the message as unverified.
- Publish exactly one record that starts with
v=spf1 - Include every service that sends as your domain
- Use at most 10 DNS lookups — beyond that SPF breaks for everyone
Check it with the SPF Checker or build a new one with the SPF Generator.
2. DKIM is not enabled
DKIM adds a cryptographic signature to each message. Most providers support it but do not switch it on automatically for custom domains. Without DKIM, forwarded mail and mail from shared services often fails authentication.
Enable it in your provider's admin panel, publish the DNS record it gives you and verify it with the DKIM Checker.
3. No DMARC record
DMARC tells receivers what to do when SPF and DKIM fail, and sends you reports. Gmail and Yahoo require it for bulk senders, and its absence is a negative signal for everyone. Start with p=none and a reporting address — see how to set up DMARC.
4. The From domain does not align
Passing SPF or DKIM is not enough for DMARC: the domain that passes must match the domain in the visible From address. A newsletter tool that sends with its own domain in the background will pass SPF for its domain, not yours. Configure a custom sending domain (often called "domain authentication") in each tool.
5. Your IP or domain is on a blacklist
If your sending IP or your domain appears on a major DNS blocklist such as Spamhaus, many receivers filter or reject your mail. Check with the Blacklist Checker and read how to get delisted.
6. No reverse DNS on your mail server
If you run your own mail server, its IP needs a PTR record whose host name resolves back to the same IP. Without it Gmail and Outlook often defer or reject mail. Test it with the Reverse DNS Lookup.
7. Sending to invalid or old addresses
High bounce rates and spam-trap hits damage your reputation quickly. Old lists contain abandoned mailboxes that some providers turn into spam traps. Verify lists before sending and remove addresses that hard-bounce.
8. People mark you as spam
Complaints weigh heavily. Gmail asks bulk senders to keep the reported spam rate below 0.3% (ideally under 0.1%). Send only to people who opted in, make your sender name recognisable and make unsubscribing easy.
9. No easy unsubscribe
Bulk marketing mail to Gmail and Yahoo must support one-click unsubscribe (the List-Unsubscribe and List-Unsubscribe-Post headers) and honour requests promptly. Most email marketing platforms add this for you — check that it is enabled.
10. Sudden volume spikes
A new domain or IP that suddenly sends thousands of messages looks like a spammer. Increase volume gradually ("warm-up") and send consistently.
11. Content and links
Content matters less than authentication and reputation, but it still counts: link shorteners, links to domains with bad reputation, image-only emails, misleading subjects and large attachments all add risk. Use your own domain in links and keep a good text-to-image balance.
12. Missing TLS
Modern providers expect mail to arrive over an encrypted connection. If you run your own server, make sure STARTTLS works with a valid certificate — test it with the SMTP Test.
A quick checklist
- Run the Domain Checker and fix every failed item
- Enable DKIM in each sending service
- Publish DMARC with a reporting address
- Check blacklists for your sending IP and domain
- Clean your list and remove hard bounces
- Watch Google Postmaster Tools for spam rate and reputation
Frequently asked questions
Why do my emails go to spam in Gmail but not in Outlook?
Each provider uses its own filters and reputation data. Gmail weighs authentication and complaint rates heavily; check DMARC alignment and your Postmaster Tools spam rate.
Will changing my subject line fix spam placement?
Rarely on its own. Authentication, reputation and list quality matter far more than individual words.
How long does it take to recover from spam placement?
Technical fixes (SPF, DKIM, DMARC) take effect within hours. Reputation recovers over days to weeks of consistent, wanted mail.