Why are my emails going to spam?

Start here: a five-minute diagnosis

Before rewriting copy or switching tools, rule out the technical causes. They are the most common, the easiest to fix, and they make every other improvement pointless if they’re broken.

1. Run a domain health check on the domain in your From address. SPF, DKIM and DMARC should all pass.
2. Run a blacklist check on the domain and its sending IPs.
3. Run an inbox placement test with the exact email you’re sending, from the exact mailbox. This shows whether you’re in spam everywhere or only at one provider, which narrows the cause sharply.
4. Read the headers of a message that landed in spam. The Authentication-Results header shows whether SPF, DKIM and DMARC passed for that provider.

Then work through the causes below in order.

The 12 most common causes, and how to fix each

1. Missing or broken authentication

Symptom: spam or rejection at most providers, especially for mail from a new sending tool. Why: large providers now require SPF, DKIM and DMARC from bulk senders, and treat unauthenticated mail with suspicion at any volume. A second SPF record, an SPF record over 10 DNS lookups, or a sending tool that signs DKIM with its own domain instead of yours are the usual culprits. Fix: one SPF record under 10 lookups, DKIM signing with your domain, DMARC published. See SPF, DKIM and DMARC explained.

2. DMARC alignment failure

Symptom: SPF and DKIM both “pass” in the headers, but DMARC fails. Why: they passed for the sending service’s domain, not for the domain in your From address. Fix: set up custom DKIM (sometimes called branded or domain authentication) in each sending tool, so the signature uses your domain.

3. A new domain or mailbox with no reputation

Symptom: a brand-new domain or mailbox lands in spam from the first campaign. Why: providers have no history to trust, and a new sender pushing volume looks like a spammer. Fix: warm up for two to four weeks before campaigns, starting at 2-5 emails a day. See the complete guide to email warm-up.

4. A sudden spike in volume

Symptom: placement was fine, then dropped right after a bigger send. Why: a jump from 30 to 300 emails a day from one mailbox, or a big launch from a quiet domain, breaks the pattern providers expect. Fix: increase volume gradually, spread it across more mailboxes, and keep each cold-email mailbox around 30-50 a day.

5. A blocklist listing

Symptom: rejections with error messages naming a blocklist, or spam placement at providers that use that list. Why: your domain or IP sent mail that hit spam traps or drew complaints, or you share an IP with someone who did. Fix: find and stop the cause first (a bad list segment, a compromised account, a misconfigured server), then request removal through the list’s own site. Listings that recur quickly are usually escalated, so fixing the cause comes before the delisting request.

6. High complaint rates

Symptom: placement declines over days or weeks despite correct setup. Why: recipients clicking “report spam”. Google and Yahoo require bulk senders to stay below 0.3% user-reported spam, and recommend well under 0.1%. Fix: send only to people who expect to hear from you, make opting out easier than reporting spam, and stop mailing people who never engage. See bulk-sender requirements.

7. Poor list quality and bounces

Symptom: high hard-bounce rates, and placement dropping across the board. Why: old, scraped or purchased lists contain invalid addresses and spam traps. Bounces tell providers you don’t know your recipients. Fix: verify addresses before sending, remove hard bounces immediately, and never send to lists collected without a lawful basis.

8. Low engagement

Symptom: you reach the inbox at first, but placement slides as a campaign runs. Why: messages that are never opened, replied to or rescued from spam teach the filter that recipients don’t want them. Fix: tighten targeting, shorten sequences to unresponsive contacts, and keep background warm-up running so a steady share of your traffic gets positive engagement.

9. Content and formatting that trips filters

Symptom: a specific message lands in spam while others from the same mailbox don’t. Why: content matters less than reputation, but it still counts. Common triggers: many links, link shorteners, image-only messages, large attachments, heavy HTML in what should be a personal note, misleading subject lines and aggressive sales language. Fix: for cold email, write short plain-text messages with at most one link and no attachments. Test variants with a placement test rather than guessing.

10. Shared tracking domains and links

Symptom: spam placement correlates with open or click tracking being on. Why: many sending tools use a shared tracking domain for links and open pixels. Its reputation is shared with every other sender on the tool. Fix: set up a custom tracking domain on your own domain, or turn open tracking off for cold outreach. Make sure every link points to a domain with a good reputation.

11. Missing reverse DNS or misconfigured servers

Symptom: rejections or spam from your own mail servers, often at strict corporate receivers. Why: sending IPs without a PTR record, or a PTR that doesn’t resolve back to the same IP, look like compromised machines. Fix: set a PTR record for every sending IP that matches a hostname pointing back to it, and make sure TLS is enabled. Email service providers handle this for their own IPs.

12. Provider-specific reputation

Symptom: fine at most providers, spam at one. Why: each provider keeps its own reputation for your domain and IPs, built from its own users’ reactions. A provider where your recipients engage least, or where your warm-up never built any history, will be the first to filter you. Fix: look at placement per provider, not the average. Build reputation with every provider your recipients use. That’s why RoxInbox’s network covers Outlook and Microsoft 365, Google Workspace, Yahoo, Zoho, iCloud, Mail.ru, Yandex, GMX and WEB.DE, and corporate SMTP, with no provider holding more than 40% of it.

Quick reference: symptom to cause

What about “spam words”?

Lists of forbidden words circulate widely. Modern filters don’t block a message because it contains “free” or “guarantee”; they weigh content alongside sender reputation, authentication and engagement. Misleading or pushy language does hurt, mostly because recipients report it. Write the way you’d write to one person you respect, and test.

Outlook junk folder: specific checks

Microsoft’s consumer mail (outlook.com, hotmail.com, live.com) is often the first place cold email lands in Junk. Beyond the general fixes:

• Make sure SPF, DKIM and DMARC all pass. Microsoft requires them from senders above 5,000 messages a day to its consumer domains.
• Check your sending IP’s data in Microsoft SNDS if you run your own servers.
• Keep volume per mailbox modest; Microsoft is quick to throttle sudden increases.
• See the Outlook and Microsoft 365 warm-up guide.

A sudden drop in open rates

Open rates are a weak signal. Privacy features in some mail apps load images automatically, inflating opens, while others block tracking pixels entirely. A sudden drop can mean spam placement, a tracking problem, or just a change in how a provider handles images. Before you act, run a placement test. If you’re in the inbox, look at the copy and targeting; if you’re in spam, work through the causes above.

Transactional email in spam

Password resets, receipts and onboarding emails landing in spam is a different and more urgent problem, because recipients actively want them. The usual causes:

• The transactional stream shares a domain or IP with marketing or cold email. Separate them, using a subdomain such as notify.yourdomain.com with its own authentication.
• The product sends from a new domain or a new email service without any warm-up. Ramp new transactional streams gradually too.
• Missing authentication on the service that sends them. Product teams often add a sending service without telling whoever manages DNS.
• Templates that look like marketing, with heavy images, many links and promotional language in what should be a short notification.

Fix these, then confirm with a placement test sent from the actual application, not from a mailbox.

How to recover

1. Stop the damage. Pause campaigns from affected mailboxes, but keep warm-up running if the cause is fixed.
2. Fix the cause using the list above. Repairing reputation without fixing the cause doesn’t last.
3. Request delisting from any blocklist once the cause is fixed.
4. Rebuild gradually. Restart at a low volume and ramp as if the mailbox were new. Recovery usually takes longer than a fresh warm-up.
5. Measure progress with placement tests, not open rates.
6. Monitor from now on. Most problems are visible days before they hurt replies, if something is watching.

RoxInbox’s deliverability monitoring gives every mailbox a health score, checks DNS and blocklists daily, and pauses a mailbox automatically when its spam rate starts to climb. For a domain that’s already in trouble, see reputation recovery.

Written by the RoxInbox team

The people who build and run the RoxInbox warm-up network, placement tests and monitoring. We write from what we see across mailbox providers every day. About the authors