In short
An email lands in spam for one of three reasons: authentication fails (SPF, DKIM, DMARC or the server PTR), reputation is poor (of the IP, the domain or the shared relay it leaves through), or the content and sending pattern look like spam. To find out which, send an email to a Gmail account, open Show original and check SPF, DKIM and DMARC. If all three say PASS and it still lands in spam, the problem is reputation, and you check it in Google Postmaster Tools.
A 5-minute diagnosis
- Send a test email, with real text and not just "test", to a Gmail account and an Outlook.com account.
- In Gmail, open the message, ⋮ menu › Show original. At the top you'll see SPF, DKIM and DMARC with PASS or FAIL.
- Check which server it left through: the first Received line shows the IP. If you see a relay such as MailChannels, your reputation partly depends on that relay's other customers.
- Look up the IP at check.spamhaus.org.
- If all three pass and the IP is clean, register your domain in Google Postmaster Tools to see its reputation and spam rate.
If you're not sure how to read what the original shows, the email headers guide explains it field by field.
The most common causes
| Cause | How to spot it | Fix |
|---|---|---|
| Missing or broken SPF or DKIM | spf=fail, softfail or none; dkim=none in the original | Set up SPF and DKIM from Email Deliverability |
| No DMARC | dmarc=none | Publish a DMARC record, at least with p=none |
| Missing or mismatched PTR | dig -x IP doesn't return the server hostname | Fix the PTR and hostname |
| IP on a blocklist | Bounces mentioning Spamhaus, Barracuda or Microsoft | Request removal after fixing the cause |
| Shared relay or IP with poor reputation | Everything passes, but the outgoing IP belongs to a shared relay | Ask your host for another outbound route or use a service with a dedicated IP |
| Damaged domain reputation | Postmaster Tools shows low reputation or a high spam rate | Move marketing to a subdomain and bring complaints down |
| Bulk mail from the main domain | Marketing campaigns use the same domain as day-to-day email | Send campaigns from a subdomain, e.g. news.yourcompany.com |
| Suspicious content | Everything passes and the IP is clean, but only some messages land in spam | Fewer shortened links and images, real text, a full signature |
| Sudden volume | A new or dormant domain suddenly sends hundreds of emails | Ramp up volume gradually over a few weeks |
What Gmail, Yahoo and Microsoft require
Since February 2024 Gmail and Yahoo, and since May 2025 Microsoft (Outlook.com and Hotmail), enforce minimum requirements on anyone sending to them. Since late 2025 Gmail rejects part of the non-compliant mail instead of just sending it to spam.
| Requirement | All senders | Over 5,000 emails a day |
|---|---|---|
| SPF or DKIM | At least one | Both |
| DMARC | Recommended | Required, at least p=none, aligned with the From |
| Valid PTR for the sending IP | Required | Required |
| Encrypted connection (TLS) | Required | Required |
| Spam rate in Postmaster Tools | Below 0.3% | Below 0.3% (ideally under 0.1%) |
| One-click unsubscribe | Not applicable | Required on marketing email |
If your host uses a shared relay
Many hosting providers route their customers' outbound mail through a relay such as MailChannels to protect their own IPs. It's good practice, but it has a side effect: Gmail sees the relay's IP, shared by thousands of senders. Your records can be perfect and you still inherit part of other people's reputation.
In that case, what you do control is your domain reputation: full authentication, DMARC with a policy, no bulk campaigns from your main domain and few complaints. If the problem persists, ask your provider for an outbound route with a better reputation.
How to look after your domain reputation
- Separate marketing. Send newsletters and campaigns from a subdomain (news.yourcompany.com) with its own SPF, DKIM and DMARC. If a campaign draws complaints, day-to-day email isn't affected.
- Measure. Google Postmaster Tools for Gmail and SNDS for Microsoft show reputation and complaint rates.
- Tighten DMARC once the reports show all your legitimate mail passes: from p=none to p=quarantine and then p=reject.
- Stop people spoofing you. A domain without a strict DMARC policy can be used in phishing campaigns, which also hurts its reputation. See domain spoofing.
Content and sending habits
- Messages with real text; an email that only says "test" or "hi" looks like a spam probe.
- A display name on the sender ("Anna Smith · Your Company"), not just the address.
- Few links, no URL shorteners, pointing to your own domain.
- Attachments in common formats (PDF), not password-protected archives or executables.
- Don't auto-forward all of the server's mail to Gmail: forwarding spam damages your server's reputation.
Frequently asked questions
My emails pass SPF, DKIM and DMARC, so why do they still go to spam?
Because authentication only proves who is sending. If the IP, relay or domain reputation is poor, or the content looks like spam, Gmail and Outlook can still junk it. Check Postmaster Tools and the outgoing IP.
How do I get my emails out of Gmail's spam folder?
Fix the cause (authentication, PTR, blocklists or reputation) and ask some recipients to mark your emails as "Not spam" and add you to their contacts. Reputation improves over days or weeks, not instantly.
Does my host using MailChannels affect my email?
It can, because the IP Gmail sees is shared by many of the relay's customers. A well-authenticated domain with a good reputation is still what matters most.
Is DMARC mandatory?
For anyone sending more than 5,000 emails a day to Gmail, Yahoo or Outlook.com, yes. For everyone else it's strongly recommended: it improves delivery and stops your domain being spoofed.
Protect inbound email on your whole server
Besides looking after what you send, protect what you receive: Clisec filters phishing, BEC fraud, spam and malware for every account on your cPanel server.