Your quote, invoice or reply never reached the customer, or it turned up in their spam folder. It's frustrating, and it usually has a clear cause. Here are the most common ones, roughly in order of how often we see them, with a way to check each.

1. Missing SPF, DKIM or DMARC records

These three DNS records prove that your email really comes from your domain. Without them, Gmail, Outlook and Yahoo can't tell your mail apart from a forgery, so they treat it with suspicion. Gmail and Yahoo have required them from bulk senders since 2024.

Check: run your domain through our free DMARC checker. It shows which records are missing and gives you the exact record to add. Setup guides: Google Workspace and Microsoft 365.

2. A service sending as you that isn't authorised

Your website's contact form, your newsletter tool or your invoicing software sends mail "from" your domain, but isn't listed in your SPF record and doesn't sign with your DKIM key. Those messages fail authentication even if your normal mailbox is fine.

Check: send a test from that tool to a Gmail address, open it, choose ⋮ → Show original, and look for SPF: PASS and DKIM: PASS. Most tools have a "domain authentication" setting that gives you the records to add.

3. Two SPF records, or too many lookups

A domain may have only one SPF record, and SPF may trigger no more than 10 DNS lookups. Break either rule and SPF fails for every message, quietly. This often happens when a new tool's setup guide says "add this SPF record" and someone adds a second one.

Check: the DMARC checker counts your SPF records and lookups.

4. Your mail server or website server is on a blocklist

If your server's IP address was used to send spam (by you, a hacked website on the same server, or a previous owner of that IP), spam blocklists may list it. Many mail providers check those lists.

Check: look up your mail server's IP on the major lists (Spamhaus, Barracuda, SpamCop). Be careful with tools that report "listed on 1 of 80 lists"; many small lists list whole hosting networks and are ignored by real mail providers. Spamhaus and Barracuda are the ones that matter most.

5. A new or rarely used domain

Mail providers trust domains with a history. A domain registered last month, or one that suddenly sends hundreds of emails after months of silence, looks like a spammer setting up. Warm up slowly: start with normal one-to-one email and increase volume gradually.

6. What's in the email

  • Link shorteners (bit.ly and similar) and links to domains with a bad reputation.
  • One big image with little text, or invoices sent as a lone attachment with an empty body.
  • Spam-style wording: "act now", "100% free", lots of capitals and exclamation marks.
  • A "From" name or address that doesn't match the domain in your links.

7. People don't open, or they mark you as spam

For newsletters and cold email, engagement matters. If many recipients delete without opening, or click "Report spam", providers send your future mail to spam for everyone. Gmail expects bulk senders to keep the spam-complaint rate below 0.3%. Always include a working unsubscribe link, and only email people who expect to hear from you.

A quick plan

  1. Check your domain and fix any missing or broken SPF, DKIM and DMARC records.
  2. Send a test to Gmail and confirm all three pass in "Show original".
  3. Authorise every tool that sends as your domain.
  4. Keep it working: records break when DNS changes hands or a tool is added. Daily Website Report checks your email setup every day, along with your website's SSL, security and uptime, and tells you in plain English when something changes. It's free for one site.