The short answer

Most business email ends up in spam for one of three reasons: the domain’s authentication records (SPF, DKIM and DMARC) are missing or wrong, the domain or sending server has a poor reputation, or the message itself looks like spam. Authentication is the most common cause for small businesses, and the easiest to fix.

1. Missing or broken SPF, DKIM and DMARC

These three DNS records let receiving services such as Gmail and Outlook check that a message really came from you.

  • SPF lists the services allowed to send email for your domain. A domain must have only one SPF record. Two records, often added by different suppliers, can break it completely.
  • DKIM adds a digital signature to each message. In Microsoft 365, DKIM has to be switched on for your own domain; it is easy to miss during setup.
  • DMARC tells receivers what to do with messages that fail those checks, and sends you reports. Without it, nothing stops someone sending fake emails in your name.

Since 2024, Gmail and Yahoo have required everyone who sends to their users to authenticate their mail, and bulk senders must have SPF, DKIM and DMARC. Microsoft has introduced similar requirements for high-volume senders to Outlook.com addresses. Domains without these records are far more likely to be filtered.

2. Sending reputation

  • A brand-new domain has no history, so filters are cautious at first.
  • Sending newsletters or bulk mail from your normal mailbox can damage the reputation of all your email. Bulk mail belongs on a proper email marketing service, set up with its own DNS records.
  • Lots of bounces or spam complaints tell receivers your mail isn’t wanted.
  • Blocklists. If your domain or the server you send through has been listed, mail can be blocked or filtered until it is removed.

3. The message itself

Content matters less than most people think, but some habits do trigger filters: link shorteners, messages that are a single image with little text, an attachment with no explanation, all-caps subject lines, or a “from” name that doesn’t match the address.

How to check your own domain

  1. Run our free email check. It shows whether your domain has MX, SPF, DKIM and DMARC records, and explains each result.
  2. Send a test to a Gmail address, open it, choose “Show original” from the menu, and look for SPF, DKIM and DMARC each showing PASS.
  3. Ask a customer whose copies went to junk which email service they use. A problem with just one provider points to reputation or a provider-specific rule.

When to get help

If the check shows anything missing, or you have more than one SPF record, the fix is usually a few careful DNS changes and switching on DKIM in your email service. Making changes in the wrong order can stop email being delivered at all, so if you are not comfortable editing DNS, get help. See fixing emails that go to spam and DMARC setup.