October 1, 2026

You wrote a clean, useful newsletter. You hit send to 2,400 subscribers. Two days later, your open rate is 6% and a client tells you they found your message in the junk folder. If your emails going to spam has become a recurring problem, it is almost never bad luck and almost always a technical or hygiene issue that can be traced and fixed. The good news: most small business deliverability problems come down to eight causes, and none of them require a developer. In this guide we explain what actually triggers the filters at Gmail, Outlook and Yahoo, and we pair every cause with a concrete fix you can complete in an afternoon. First, confirm you really have a spam problem Before you change anything, diagnose. Rebuilding your templates when the real issue is a broken SPF record is wasted effort. The 15-minute diagnostic Send a test to yourself on three providers: one Gmail address, one Outlook/Hotmail address, one address on your own domain. Where does it land? Open the message and check the headers. In Gmail, click the three dots and choose Show original. You want to see SPF: PASS, DKIM: PASS and DMARC: PASS. Anything else is your first fix. Run a free seed test with a tool such as Mail-Tester, GlockApps or MxToolbox. A score below 8/10 tells you where to start. Check your spam complaint rate in your email platform. Above 0.1% is a warning. Above 0.3% and mailbox providers will start filtering you by default. Use this table to match symptoms with likely causes: Symptom Most likely cause Fix below Every recipient, every provider, junk folder Authentication failing or domain blacklisted Fix 1, 2, 3, 8 Only Gmail filters you Low engagement, complaints, missing one-click unsubscribe Fix 5, 6, 7 Only Outlook/Microsoft filters you IP reputation, 2025 Microsoft sender requirements Fix 1, 2, 3, 8 Transactional emails fine, newsletters filtered List quality and content Fix 4, 5, 6 Problem started suddenly DNS change, new sending tool, purchased list, volume spike Fix 1, 4, 8 Fix 1: Publish a correct SPF record SPF (Sender Policy Framework) is a DNS record that lists which servers are allowed to send email using your domain. If Mailchimp, Brevo, HubSpot or your CRM is not listed, receiving servers see a mismatch and your emails going to spam becomes the default outcome. What to do Log in to wherever your domain DNS is managed (registrar or hosting panel). Look for an existing TXT record starting with v=spf1. Add the include mechanism your email provider gives you. Merge everything into one single SPF record. End with ~all (softfail) or -all (hardfail) once you are confident every sender is listed. Example of a valid merged record: Type TXT Host / Name @ Value v=spf1 include:_spf.google.com include:spf.mandrillapp.com ~all TTL 3600 Two mistakes to avoid: never publish two separate SPF records on the same domain (that is an automatic fail), and stay under the limit of 10 DNS lookups. Fix 2: Turn on DKIM signing DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each message so the receiving server can verify the email was not altered and genuinely comes from your domain. Gmail, Yahoo and Microsoft now expect it from anyone sending in volume. This is treated carefully on adhurl.com. What to do Open your sending platform and find the section called Authenticate domain, Domain verification or Sending domains. Copy the CNAME or TXT records it generates. They usually look like s1._domainkey and s2._domainkey. Paste them into your DNS exactly as provided, with no trailing dots or extra spaces. Click Verify in the platform. Propagation is usually minutes, sometimes a few hours. If you use several tools (a newsletter platform, a CRM, an invoicing app, a helpdesk), each one needs its own DKIM selector. Do them all in the same session so nothing is left unsigned. Fix 3: Add a DMARC record and read the reports DMARC tells mailbox providers what to do when SPF and DKIM fail, and it sends you reports showing who is sending on behalf of your domain. Since the 2024 Gmail and Yahoo bulk sender rules, and Microsoft’s own tightening in 2025, a domain without DMARC is treated with suspicion. Start in monitoring mode Type TXT Host / Name _dmarc Value v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; fo=1 Leave it at p=none for two to four weeks while you confirm every legitimate sender passes. Then move to p=quarantine, and later p=reject once reports are clean. Free report readers such as Postmark’s DMARC digest or Valimail Monitor turn the raw XML into a readable summary. Fix 4: Stop sending marketing mail from a free address or a brand new domain Sending a campaign with a From address like yourbusiness@gmail.com through a third-party platform breaks DMARC alignment, because Gmail’s own DMARC policy says nobody else may send as gmail.com. That single mistake can send an entire campaign to junk. Related reading: Why do emails land in the spam folder. What to do Always send from your own domain: hello@yourcompany.com. Consider a dedicated subdomain for marketing, such as news.yourcompany.com, so a bad campaign never damages the reputation of your invoices and client replies. Never use noreply@. It suppresses replies, and replies are one of the strongest positive engagement signals a mailbox provider can see. If your domain is brand new, expect filtering. Domain age matters. Warm it up slowly (see Fix 8) rather than blasting 5,000 contacts on day one. Fix 5: Clean your list, then keep it clean Poor list hygiene is the number one non-technical reason for emails going to spam. Old addresses turn into spam traps. Hard bounces signal you are mailing a purchased or scraped list. Subscribers who have ignored you for 18 months drag your engagement rate down and teach Gmail that your mail is unwanted. Your afternoon clean-up Export your list and run it through a verification service (ZeroBounce, NeverBounce, Bouncer). Remove invalid, catch-all risky and role addresses such as info@, contact@, sales@ where you have no