You write a newsletter, press send, and then a subscriber replies: “Found this in my spam folder.” Your open rates drop, your sales emails go unseen, and you are not sure whether the problem is your content, your email platform or something technical you have never heard of.
Spam-folder problems feel mysterious, but mailbox providers such as Gmail, Outlook and Yahoo follow fairly consistent rules. They ask three questions about every email: Is the sender who they claim to be? Do recipients want these emails? Does the message look like spam? Fix the answers to those three questions and most deliverability problems disappear.
In this article
Why emails land in spam: the 5 usual causes
- Missing authentication. Without SPF, DKIM and DMARC records, mailbox providers cannot verify that you are allowed to send from your domain. Since 2024, Gmail and Yahoo have required authentication for bulk senders, and unauthenticated mail is far more likely to be filtered.
- Sending from a free address. Sending newsletters “from” a gmail.com or yahoo.com address through a marketing platform fails authentication checks, because those domains do not authorise your platform to send for them.
- A dirty list. Old addresses, typos, abandoned inboxes and spam traps cause bounces and complaints. High bounce and complaint rates damage your sender reputation.
- People who never asked. Bought lists, scraped contacts and “imported from my phone” lists generate spam complaints. Even a small complaint rate hurts.
- Content and format signals. Misleading subject lines, all-caps, a single large image with little text, too many links, or link shorteners can push a borderline email into spam.
Diagnose it in 10 minutes
| Test | How | What a problem looks like |
|---|---|---|
| Authentication | Send an email to a Gmail address, open it, choose “Show original” | SPF, DKIM or DMARC shows FAIL or is missing |
| From address | Look at your platform’s sender settings | You send “from” @gmail.com or @yahoo.com |
| Bounce rate | Your platform’s campaign report | Above about 2% |
| Complaint rate | Campaign report or Gmail Postmaster Tools | Approaching 0.1%, and well above 0.3% is serious |
| Engagement | Open and click rates by segment | Most of the list has not opened in 6+ months |
| Content | Send a test to several inboxes and a spam-checker tool | One large image, spammy words, broken links |
Gmail Postmaster Tools is free and shows your domain’s reputation and spam rate once you send enough mail to Gmail users.
The 15 fixes, in order of impact
Authentication and setup
- Send from your own domain. Use an address such as hello@yourbrand.com, not a free mailbox. Your email platform will ask you to verify it.
- Add SPF. A DNS record listing the services allowed to send email for your domain. Your platform gives you the exact value to add at your domain registrar or host.
- Add DKIM. A digital signature that proves your emails were not altered. Your platform provides one or more DNS records; add them exactly as shown.
- Add DMARC. A record that tells mailbox providers what to do if SPF or DKIM fail, and sends you reports. Start with a monitoring policy (
p=none) and tighten it later once everything passes. - Align your domains. The domain in your “From” address should match the domain that is authenticated. Most platforms guide you through this.
- Add one-click unsubscribe. Large mailbox providers expect a visible unsubscribe link and the list-unsubscribe header. Reputable platforms add both automatically.
List quality
- Use confirmed opt-in for new subscribers if you have problems with fake or mistyped addresses. It slows growth slightly but greatly improves list quality.
- Remove hard bounces immediately. Most platforms do this automatically; check that the setting is on.
- Sunset inactive subscribers. Send a re-engagement email to people who have not opened or clicked in 90 to 180 days, then remove those who still do not respond.
- Never use bought, rented or scraped lists. Besides spam complaints, they can contain spam traps that damage your reputation quickly.
- Protect your sign-up forms. Add a hidden honeypot field or a CAPTCHA to stop bots filling your list with fake addresses.
Content and sending habits
- Write honest subject lines. The subject should describe what is inside. Avoid all-caps, excessive punctuation and “RE:” tricks.
- Balance text and images. Include real text, not one large image. Make sure every image has alt text.
- Use full, branded links. Avoid public link shorteners; link to your own domain where possible.
- Send consistently. Sudden huge sends after months of silence look suspicious. If you have a new domain or a long break, warm up gradually: start with your most engaged subscribers and increase volume over a few weeks.
When your email platform is part of the problem
Sometimes the platform you use makes good deliverability harder: authentication is hard to set up, you cannot remove inactive subscribers easily, or the shared sending servers have a poor reputation. In that case, moving to a platform with guided authentication and good list tools is worth it.
| Need | Platform | Why |
|---|---|---|
| Newsletters plus transactional emails, generous free tier | Brevo | Clear domain authentication steps and both marketing and transactional email in one account |
| Newsletter-first publishing and growth | beehiiv | Built for newsletters, with authentication, list cleaning and growth tools |
Whichever you choose, the fixes above still apply: a new platform does not fix a bought list.
A real-world example
A small online course creator noticed open rates falling from around 40% to under 15% within two months. “Show original” in Gmail revealed DKIM was missing after a switch of email platform. After adding the DKIM records and a DMARC record, removing about a fifth of the list that had not opened in six months, and sending a short “are you still interested?” email to the rest, open rates recovered over the following four weeks. Nothing about the content changed: the problem was entirely technical and list-related.
How to stop it happening again
- Check your authentication after every DNS or domain change.
- Review bounce and complaint rates after every campaign.
- Clean inactive subscribers every quarter.
- Keep a predictable sending rhythm, such as weekly on the same day.
- Watch Gmail Postmaster Tools once a month.
- Make it easy to choose fewer emails: a preference centre reduces unsubscribes and complaints.
Frequently asked questions
Why do my emails go to spam in Gmail but not elsewhere?
Gmail weighs engagement and authentication heavily. Check that SPF, DKIM and DMARC pass in “Show original”, and remove subscribers who never open.
Do certain words send emails to spam?
Single words rarely decide it on their own today. Misleading subject lines, poor reputation and missing authentication matter far more. Still, avoid hype such as “100% free money”.
How long does it take to fix a bad sender reputation?
Usually several weeks of authenticated, consistent sending to engaged subscribers. There is no instant reset.
Should I ask subscribers to whitelist me?
Yes. Ask new subscribers in the welcome email to add your address to their contacts or move your email to the primary inbox.
Does my email platform affect deliverability?
Yes, partly. Platforms differ in how easy they make authentication, how they handle bounces and how they protect their shared sending reputation. But even the best platform cannot rescue a list of people who never asked to hear from you.
Is the Promotions tab the same as spam?
No. Emails in Gmail’s Promotions tab are delivered and can be opened; spam is filtered out of the inbox entirely. Promotions placement is normal for marketing emails.
Fix authentication today, clean your list this week, and keep sending emails your subscribers actually want. Deliverability follows.