- Authentication (SPF, DKIM, DMARC) is the baseline.
- List quality matters more than content tricks.
- Complaints and bounces damage reputation quickly.
- Warm up new domains and keep volume steady.
Why mail goes to spam
Mailbox providers score each message on sender reputation, authentication, recipient engagement and content. A weak score on any of these can send mail to spam or reject it.
Fix authentication first
| Record | What it does |
|---|---|
| SPF | Lists the servers allowed to send for your domain |
| DKIM | Signs messages so receivers can detect tampering |
| DMARC | Tells receivers what to do when SPF or DKIM fails and reports results |
Large providers publish requirements for bulk senders; see Google's guidelines linked below and our deliverability guide.
Keep your list and content clean
- Email only people who opted in.
- Remove hard bounces and long-inactive contacts.
- Make unsubscribing easy.
- Match the subject line to the content.
- Avoid link-only emails and URL shorteners from unknown domains.
Send steadily
Sudden jumps in volume look suspicious. Raise volumes in steps, especially on a new domain, and watch complaint rates after each send. A dedicated sending address for marketing keeps transactional mail safe. See our transactional email service for that split.
A diagnosis path
- Send a test to Gmail, Outlook and another provider and note where each lands.
- Open the full headers of the received message and look for SPF, DKIM and DMARC passing.
- Check bounce and complaint figures in your sending reports.
- Review the list source and last-engagement dates.
- Compare the content with recent mail that did reach the inbox.
What not to do
- Do not buy or rent email lists.
- Do not hide the unsubscribe link.
- Do not switch sending domains to escape a bad reputation; fix the cause.
- Do not send one large blast after months of silence.
Recovering after a problem
Pause marketing sends, send only to your most engaged contacts for a few weeks, fix authentication and remove addresses that bounce. Increase volume gradually once complaints are low. Recovery takes weeks, not hours.
Sources and further reading
Rules and platform requirements change. Last reviewed . This guide is general information, not legal advice.