“My emails are going to spam” is the single most common thing we hear from small businesses — and it’s also one of the most misunderstood problems in email.

Most people assume it’s one issue with one fix. In reality, it’s usually one of five or six distinct causes, each with a completely different solution. Fixing the wrong one wastes time and doesn’t move the needle.

This checklist walks through them in the order we’d actually diagnose them — starting with the most common.

By far the most frequent cause. If your domain doesn’t correctly prove it’s really you sending the email, inbox providers treat that as a strong spam signal — sometimes strong enough on its own to guarantee the spam folder, regardless of how good your content is.

How to check: send a test email to a Gmail address you control, open it, click the three dots, and select “Show original.” Look for SPF: PASS, DKIM: PASS and DMARC: PASS. Any FAIL is a direct cause of deliverability problems.

If this is the issue, our guide on what SPF, DKIM and DMARC actually mean explains what each check verifies and why they’re commonly misconfigured.

Every domain and sending server builds up a reputation over time, based on how recipients interact with your email — opens, replies, deletions, and crucially, spam complaints. If a previous owner of your domain sent spam, if a colleague’s email was compromised and used to send junk, or if you’ve sent to a purchased or outdated list that generates complaints, that reputation damage lingers and affects deliverability even for genuine messages.

How to check: tools like Google Postmaster Tools (for domains sending meaningful volume to Gmail) show your domain’s reputation directly. A consistently poor or declining score points here.

Reputation damage is slow to build and slow to repair — this is usually the issue when authentication passes perfectly but deliverability is still poor.

Spam filters also read the email itself. Certain patterns are still reliably flagged: excessive capital letters, multiple exclamation marks, an image-only email with almost no text, a poor text-to-link ratio, or subject lines using classic trigger phrases (“Act now,” “100% free,” “Limited time”). This matters more for marketing sends than for one-to-one business correspondence, but it’s worth ruling out for newsletters or automated sends.

How to check: if the problem is isolated to one type of email (e.g. your newsletter but not your invoices), content is a likely factor rather than authentication.

Gmail and Outlook increasingly personalise spam filtering per recipient based on how that specific person treats your previous emails. If someone has ignored, deleted without opening, or previously marked a message from you as spam, future emails to that same address are more likely to be filtered — even if everything else about your setup is correct.

This is why “it goes to spam for some customers but not others” is a genuinely common and genuinely confusing symptom — it isn’t inconsistent, it’s personalised, and it means the fix has to happen per-relationship (asking that recipient to whitelist you) rather than at the domain level.

If you’ve recently switched email or marketing platforms, started sending significantly more email than usual, or are sending from a brand-new domain with no sending history, filters treat that as inherently riskier — not because anything is wrong, but because they have no track record to trust yet. This is sometimes called a “cold” domain or IP.

How to check: did the spam problem start right after a platform switch, a big send (e.g. a mass announcement), or setting up a brand-new domain? If so, this is very likely the cause, and it typically resolves with a gradual “warm-up” period of consistent, low-volume sending rather than a one-off technical fix.

In more severe cases, your sending IP or domain may have been added to a public blocklist (such as Spamhaus) — usually as a result of one of the causes above going unaddressed for a while. This is the most serious version of the problem, because being blocklisted can cause near-total delivery failure rather than just spam-folder placement.

How to check: free blocklist-lookup tools (search “MXToolbox blacklist check”) will tell you immediately if your domain or IP is listed anywhere, and most will also tell you which one to petition for removal.

In practice, these causes often stack: a domain with weak authentication (#1) is more likely to accumulate reputation damage (#2), which increases the odds of ending up on a blocklist (#6). That’s why a proper diagnosis checks all of them in sequence rather than guessing at one and hoping.

If you’ve been through this checklist and you’re still not sure which applies to you — or you’ve identified the issue but aren’t confident fixing SPF, DKIM, DMARC records or petitioning a blocklist yourself — that’s exactly the kind of diagnosis-plus-fix work we do for small UK businesses.

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We provide:

• Free initial assessment
• Clear explanation of the issue
• Fixed-price solutions
• UK-based support

If your emails are going to spam, we can identify the cause and fix it properly.