First: one recipient, or everyone?
- One recipient or one company: their filters have taken against you. Ask them to mark a message as “not junk” and add you to their contacts or safe senders. Their IT team may also have a rule catching you.
- Lots of recipients, especially on Gmail or Outlook.com: the problem is how your mail is sent and authenticated. Work through the causes below.
1. SPF, DKIM or DMARC missing or broken
These three DNS records let receiving servers check that a message claiming to be from your domain really is. Without them — or with a mistake in them, such as an SPF record that does not include a service you send through — your mail looks no different from forgery. This is the single most common cause, and the quickest to check.
Run your domain through our free email security checker. It checks all three and explains any problem in plain English. The SPF checker also counts the 10-lookup limit, which quietly breaks SPF for many businesses that use several sending services.
2. A service sending as you without being set up
Your invoicing system, CRM, website form or newsletter tool may send email from your address. Unless each one is authorised for your domain — usually by adding a DKIM record it gives you — those messages fail authentication even if your own mailbox passes. DMARC reports show every service sending as you; our DMARC report analyser makes them readable.
3. Sending bulk email from your normal mailbox
Newsletters, mail merges and big BCC lists sent from Outlook look like spam to receiving servers, and they can harm your normal day-to-day mail too. Use a proper email marketing service for anything bulk, set it up with DKIM on your domain, and include a working unsubscribe link. Gmail requires one-click unsubscribe from senders of more than 5,000 messages a day.
4. Your domain or server’s reputation
- A new domain has no history, so providers are cautious at first. Start with normal, low-volume conversations rather than a mailshot.
- A blocklisted server — common with cheap shared hosting email — drags everyone on it down. Bounce messages mentioning a blocklist are the clue; our bounce-back guide explains them.
- Spam complaints: every recipient who marks you as spam counts against you. Only email people who expect to hear from you.
5. The message itself
Content matters less than it did, but these still raise suspicion:
- Link shorteners and links whose text shows one address but goes to another.
- A Reply-To address on a different domain from the From address.
- A message that is one big image with little text.
- Attachments such as zipped or macro-enabled files.
How to see why a message went to spam
Send a test to a personal Gmail account. Open it, select the three dots and Show original: Gmail lists whether SPF, DKIM and DMARC passed. Copy the full headers into our email header analyser to see the details in plain English.