In this guide · 8 sections
Short answer
Gmail sends mail to spam when it fails SPF or DKIM, isn't aligned for DMARC, or gets too many spam reports. Fix authentication first, then set up Google Postmaster Tools to watch your spam rate: Google says keep it below 0.1% and never reach 0.3%. Newsletters also need one-click unsubscribe.
How Gmail decides what goes to spam
Google publishes its rules in the Email sender guidelines. Since February 2024, every sender to personal Gmail accounts must meet a basic set of requirements, and anyone sending more than 5,000 messages a day to Gmail must meet a stricter set. Messages that fail can be marked as spam or rejected outright with errors such as 5.7.26.
| Requirement | All senders | 5,000+ a day to Gmail |
|---|---|---|
| SPF or DKIM | SPF or DKIM | Both SPF and DKIM |
| DMARC record | Recommended | Required (p=none is allowed) |
| From: domain aligned with SPF or DKIM | Recommended | Required |
| Valid forward and reverse DNS (PTR) | Required | Required |
| TLS when sending | Required | Required |
| User-reported spam rate | Below 0.3% | Below 0.3% |
| One-click unsubscribe for marketing | Not required | Required |
Authentication is the foundation and works the same for every mailbox provider. If you have not set up SPF, DKIM and DMARC, start with our SPF, DKIM and DMARC guide, then come back here for the Gmail-specific parts.
The spam rate: 0.1% is the real target
Gmail watches how often recipients click Report spam on your messages. Google's sender guidelines FAQ says senders should keep their user-reported spam rate below 0.1% and prevent it from ever reaching 0.3%. The effect is graduated: above 0.1% already hurts inbox placement for bulk senders, and at 0.3% or more, bulk senders are no longer eligible for help from Google.
In plain numbers, 0.1% is one complaint per 1,000 messages delivered to the inbox. A newsletter to 2,000 Gmail addresses that gets three spam reports is already over the line. That is why a single badly targeted campaign to an old list can drag down your normal invoices and replies too, if they share the same domain.
Set up Google Postmaster Tools
Postmaster Tools is Google's free dashboard for senders. It only reports on mail sent to personal Gmail accounts, and it needs some volume before it shows data, so very small senders may see little. It is still worth setting up once.
Sign in with a Google account
Any Google account or Google Workspace account works. Use a shared admin account the business owns, not a staff member's personal Gmail.
Add your sending domain
Add the domain in your From: address, for example yourcompany.com. Add subdomains you send newsletters from separately.
Verify with a DNS TXT record
Postmaster Tools gives you a TXT record. Add it at your DNS host, then click Verify. It can take a while for DNS to update.
Wait for data
Google says dashboard data is typically updated within 24 hours and that changes can take up to 7 days to show in the compliance view.
Check the compliance status page monthly
It shows pass or fail for SPF and DKIM, DNS records, TLS, message format and spam rate, plus DMARC and unsubscribe checks for bulk senders.
The Postmaster Tools dashboards also include spam rate, IP and domain reputation, authentication results, encryption and delivery errors. If your spam rate is low but reputation is poor, Google notes that Gmail may already be filtering most of your mail to spam, so few recipients see it to report it.
Forwarding, aliases and other Gmail traps
Some spam problems come from how mail travels, not what it says. Common Gmail-specific causes:
- Forwarding from another mailbox into Gmail can break SPF, because the forwarding server is not in your SPF record. Google's forwarding best practices recommend relying on DKIM, which usually survives forwarding;
- Website contact forms that send 'from' the visitor's Gmail address fail DMARC, because your server is not allowed to send as gmail.com. Send from your own domain and put the visitor in Reply-To;
- New sending tools such as a booking system or CRM sending as your domain without their DKIM set up;
- Old lists with many dead or unengaged addresses, which raise complaints and bounces;
- Link shorteners and image-only emails, which look like typical spam;
- Gmail From: impersonation: Google says it is moving gmail.com to DMARC quarantine, so never send bulk mail with a gmail.com From address through another service.
If mail is rejected rather than filtered, the bounce message carries a code such as 5.7.26 or 5.7.25. Our bounce-back errors guide explains what each one means.
What not to do
A lot of advice online makes Gmail problems worse. Avoid these:
Gmail spam mistakes to avoid
Recovery takes time. Google says it can take up to 7 days for spam rate changes to show as compliant, and reputation recovers only as recipients engage with your mail again.
Do it yourself or get help?
If you are comfortable with DNS, you can fix authentication, verify Postmaster Tools and move newsletters to a proper tool in an afternoon. The hard part is finding every service that sends as your domain: accounting software, booking tools, website forms and CRMs.
Our Emails Land in Spam Fix (S$249) inventories every sender, sets up SPF, DKIM and DMARC correctly, checks blacklists and monitors DMARC for 14 days before moving to enforcement. If your domain's DNS is a mess or sits with an old agency, Domain and DNS Setup (S$99) puts it in your name and tidies the records first.
Frequently asked questions
Gmail and Outlook use different signals. Gmail puts heavy weight on user spam reports, DMARC alignment and its own domain reputation, which Postmaster Tools shows. A domain can pass Outlook's filters and still fail Gmail if recipients report its newsletters as spam or if one sending service lacks DKIM. Check authentication first, then your Gmail spam rate.
Google's sender guidelines require senders to keep the user-reported spam rate shown in Postmaster Tools below 0.3%. Google's FAQ goes further and recommends keeping it below 0.1%, because rates above 0.1% already hurt inbox delivery for bulk senders. At 0.3% or above, bulk senders cannot get mitigation help from Google.
Yes. Postmaster Tools is free and needs only a Google account and the ability to add a TXT record to your domain's DNS. It reports on mail sent to personal Gmail accounts, not Google Workspace accounts, and it needs a reasonable daily volume before dashboards show data, so very small senders may see gaps.
Google's requirement for one-click unsubscribe applies to bulk senders of 5,000 or more messages a day to Gmail. Smaller senders are not strictly required to add it, but it still helps, because people who cannot easily unsubscribe often press Report spam instead. Any proper newsletter tool adds the headers automatically.
Once the cause is fixed, Google says compliance data can take up to seven days to update. Reputation recovers gradually as recipients open and reply to your messages without reporting them. Expect one to a few weeks of steady, wanted email. Sending a large campaign during recovery usually sets you back.