Why your business emails land in spam.

By Iain, Braw · 4 November 2026

When quotes and invoices land in customers’ junk folders, there is a short list of causes to check: missing or broken email records, a website or app sending as you without being set up, a problem with your sending reputation, or how the email itself is sent. Here is how to find which one, starting with a two-minute test.

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  • Works for Microsoft 365 and Google Workspace
  • A two-minute test to start

First, a two-minute test.

Send an ordinary email from your business address to a personal Gmail account. Open it in Gmail on a computer, click the three dots beside the reply arrow, and choose Show original. Near the top, Gmail lists three results:

SPF:   PASS with IP 40.107.xx.xx
DKIM:  PASS with domain yourdomain.co.uk
DMARC: PASS

Anything other than PASS on all three points straight at the cause. Check that the DKIM line names your own domain, too: a pass for onmicrosoft.com or a sending service’s domain means DKIM has not been set up for you. If they all pass and the email still went to spam, the problem is further down this list.

Repeat the test for every system that emails customers in your name: your accounts software, booking system, website contact form and newsletter tool. Each one is a separate sender and can fail on its own.

The causes, in the order to check them.

SPF or DKIM missing or broken

Google requires every sender to have at least one of them. Faults to look for: no DKIM because it was never switched on in Microsoft 365, two SPF records on one domain (which makes both invalid), or more than the 10 DNS lookups SPF allows.

A system sending as you that isn’t set up

Invoicing, booking and CRM tools can send “from” your address. Unless each one is in your SPF record and signs with DKIM for your domain, receivers treat its email as a possible forgery.

Your website’s contact form

WordPress sends form emails straight from the web server unless it is set up otherwise. Unless that server is in your SPF and signs with DKIM for your domain, receivers treat the email as unauthenticated. Sending through an authenticated email service fixes it.

Newsletters from your own mailbox

Sending a mailing to hundreds of people from Outlook or Gmail, in BCC, can look like spam to receivers and can affect your everyday email too. A newsletter service set up with your domain’s DKIM keeps the two apart.

People marking you as spam

Google asks senders to keep their spam complaint rate below 0.1%, and never to let it reach 0.3%. Mailing people who did not ask for it, or making it hard to unsubscribe, pushes it up, and a high rate can lead receivers to filter everything from the domain.

A blocklisted server or domain

If your email goes through shared hosting, the server may be on a blocklist because of another customer. Spamhaus and other lists have free lookup pages for your domain and the sending server’s IP address.

The email itself.

Some things in the message itself can count against it: a link shortener in place of your own links, an email that is one big image with no text, or an unusual attachment type.

A brand-new domain has no sending history for receivers to judge it by, so its first weeks of email can be filtered more strictly.

Fixing it, step by step.

Start with whatever failed the Gmail test. For SPF and DKIM, our SPF, DKIM and DMARC guide has the records for Microsoft 365 and Google Workspace and the mistakes to avoid. Then:

  • Add every service that sends as your domain to SPF, keeping it to one record.
  • Switch on DKIM in your mailbox provider and in each sending service.
  • Move website form emails onto an authenticated email service.
  • Send newsletters through a newsletter tool, only to people who asked for them, with an unsubscribe link.
  • Publish DMARC at p=none and read the reports, so you can see any sender you missed.

Changes to DNS records take effect within minutes to a couple of days. Repeat the Gmail test afterwards for each sender.

Spam folder questions

Ask us something else
Why do my emails go to spam for some people and not others?

Each provider filters differently, and individual users train their own filters. If Outlook.com users see you in Junk but Gmail users do not, run the test on an Outlook.com address too: look at the message headers for the Authentication-Results line.

Will asking customers to add me to their contacts fix it?

For that customer, it can. It does not fix the cause, and every new customer would have to do the same.

Is my domain blacklisted?

Possibly. Check the domain and the sending IP address on Spamhaus’s free lookup page.

Can you check this for me?

Yes. The free website and email check looks at your SPF, DKIM and DMARC and tells you what to fix first.

Next steps

Do small businesses need DMARC? What the rules require, and why it is worth it anyway. SPF, DKIM and DMARC explained A plain-English guide to the three records behind your email. Free website check Speed, SEO basics and email, checked for free. IT support Microsoft 365, email security and backups, looked after.

Find out what is failing.

Send us your domain and the name of any system that emails customers for you. We will find what is failing and tell you how to fix it.

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