Why your emails are going to spam and 10 real fixes

Your emails are landing in spam, and you probably don’t know it. According to Validity’s 2025 Email Deliverability Benchmark, roughly one in six emails never reach the inbox. Recipients rarely tell you when this happens. They just never see your message, and you’re left wondering why no one replies.

The fix usually comes down to authentication and sender reputation, sometimes content, sometimes engagement. Below, I’ll walk through how to diagnose the problem, then cover the 10 most common reasons emails go to spam with the specific steps to get back into the inbox.

How to tell if your emails are going to spam

To stop your emails from going to spam, set up proper domain authentication (SPF, DKIM, and DMARC), clean up your mailing list, avoid spam-trigger words or excessive links, and test your setup using a diagnostic tool like Mail-Tester before sending out messages. But first, you have to confirm the problem actually exists.

The simplest method is sending test emails to your own accounts across Gmail, Outlook, and Yahoo. Check which folder each email lands in. If you’re in spam on one provider but not another, that tells you something specific about how that provider views your sending reputation. One caveat: avoid testing by sending to another address on the same domain (e.g., info@ to bob@). The receiving mailbox sees a message from itself that it didn’t send, suspects spoofing, and flags it as spam, giving you a false positive.

Mail-Tester is a free tool that scores your email on a 10-point scale and flags authentication or content issues. GlockApps offers more detailed inbox placement reports. Google Postmaster Tools shows your domain reputation and spam complaint rate for Gmail recipients specifically.

If you don’t want to use external tools, watch your open rates closely. A sudden drop, say from 45% to 12% over a week, often signals that your emails moved from the inbox to spam. Recipients rarely tell you when this happens, so you have to catch it yourself.

One more thing worth knowing: under current Google and Microsoft rules, badly non-compliant bulk senders don’t just land in spam. Messages that fail authentication or trip the spam rate threshold are now getting 5xx permanent rejections at the SMTP level, not just filtered to the spam folder. On the Microsoft side, non-compliant bulk mail to Outlook, Hotmail, and Live.com addresses now returns a 550 5.7.515 error and is permanently rejected. So if “check spam folder” diagnostics come up empty but your emails still aren’t arriving, look at your bounce logs for 5xx errors. The message may never have reached the recipient at all.

How email spam filters actually work

Spam filters evaluate several signals before deciding where to place your email. They don’t just look at one thing in isolation.

Filters weigh all of the signals above together. You might have perfect authentication but still land in spam because recipients never open your emails. Or your content might be clean, but your domain is on a blocklist. Each of the 10 fixes below addresses a different signal.

This article focuses on diagnosing and fixing a spam problem you already have. For the full setup behind each of these signals, see our complete email deliverability guide.

10 reasons your emails are going to spam and how to fix each one

1. Missing or broken email authentication

Mail servers check whether you’re authorized to send from your domain. Without proper authentication, your emails look suspicious, and most providers will either reject them outright or route them to spam.

Here’s what each authentication protocol does.

SPF lists the servers allowed to send for your domain, DKIM proves the email wasn't altered in transit, and DMARC tells receivers what to do when those checks fail. Gmail, Yahoo and Microsoft all require this baseline. Our email deliverability guide explains how to set up each one.

To fix authentication issues, publish SPF, DKIM, and DMARC records in your DNS settings. Many email service providers handle this automatically when you connect your domain. You can verify your setup using MXToolbox or Mail-Tester.

2. Poor sender and domain reputation

Mailbox providers assign reputation scores to domains and IPs based on past sending behavior. A low score increases spam placement, even when your content is perfectly fine.

You can check your reputation using Google Postmaster Tools (for Gmail) or Talos Intelligence (for broader IP reputation). If your score is low, stop sending to unengaged contacts immediately. Then warm up your domain gradually by sending small volumes to engaged recipients first.

3. Spam trigger words and risky content

Certain words and formatting patterns raise red flags for spam filters. This doesn't mean you can never use the word “free,” but stacking multiple triggers in one email increases risk. Our list of spam trigger words covers the words to avoid and safer alternatives.

Common triggers include:

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  Words like “guaranteed,” “act now,” “winner,” “click here”

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  ALL CAPS subject lines or multiple exclamation marks

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  Image-only emails with no text

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  URL shorteners or large attachments

The fix here is straightforward: write like you’re emailing a colleague and limit links to two or three per email. Avoid attachments in cold outreach entirely, since they’re a major red flag. Keep formatting clean, too: heavy HTML, colored fonts, and oversized images all add to the risk score.

4. High complaint and spam report rates

When recipients mark your emails as spam, mailbox providers penalize your sender reputation. According to Google’s email sender guidelines, user-reported spam rates greater than 0.1% already have a negative impact on inbox delivery for bulk senders, and rates of 0.3% or higher have an even greater negative impact. Google’s own guidance sets a hard ceiling of 0.3% and recommends staying under 0.1%.

The fix is to email only people who expect to hear from you. Make unsubscribe easy and visible. Segment your audience so messages are relevant to each group, because irrelevant emails get marked as spam more often.

5. Sending from a free email address

Gmail, Yahoo, and Outlook have strict DMARC policies that cause emails sent “from” their domains via third-party tools to fail authentication. If you’re sending cold outreach from a @gmail.com address through any platform, your emails will likely fail authentication checks.

The fix is to use a custom business domain. For cold outreach at scale, this is non-negotiable. And it’s not just Google and Yahoo enforcing this. Starting May 2025, Microsoft requires SPF, DKIM, DMARC, and one-click unsubscribe for Outlook.com, Hotmail, and Live.com senders. This applies to anyone sending 5,000 or more messages per day to those consumer Microsoft domains. Authentication alignment across all three major providers is now table stakes.

6. Unclean lists and high bounce rates

Sending to invalid or outdated addresses causes hard bounces. Too many bounces quickly damage your sender reputation, and once that happens, even your emails to valid addresses start landing in spam.

The fix is to verify email addresses before sending. Remove bounces immediately after each campaign. Avoid purchased or scraped lists entirely, since they typically contain high percentages of invalid addresses.

Tip: Email verification tools can catch invalid addresses before you send. lemlist’s waterfall enrichment pulls verified emails from multiple data providers to reduce bounce rates before your campaign even starts.

7. Low open and reply rates

Mailbox providers track engagement. If recipients consistently ignore your emails, future messages are more likely to land in spam. Gmail in particular uses engagement signals heavily when deciding inbox placement.

The fix is to improve subject lines, personalize content, and send at times when recipients are likely to check email. After several attempts with no engagement, stop emailing those contacts. Continuing to send to people who ignore you hurts your reputation with everyone else.

8. Inconsistent or spiky sending volume

Sudden spikes in volume look like spam behavior to filters. Sending 500 emails on day one from a new domain is one of the most common mistakes we see.

The fix is to ramp up volume gradually over several weeks, starting with a handful of emails per day from a new inbox. lemlist recommends staying under 40 emails a day per email account and 120 a day across the sending domain, warmup included. Keep daily sending consistent rather than sending in large batches followed by silence.

9. Skipping domain and inbox warmup

New domains and inboxes have no reputation, so filters treat them with suspicion by default. Warmup builds that reputation by exchanging real emails with real inboxes before you launch campaigns. Our email warmup schedule shows how to do it in 3 to 5 weeks.

The fix is to use a warmup tool or manually warm up over several weeks. lemwarm, included with lemlist, automates this by exchanging emails with a network of real inboxes at a controlled pace. You can also warm up manually by sending small volumes of emails to contacts who will open and reply.

10. Landing on an email blocklist

Blocklists are databases of IPs and domains flagged for spam. If your domain or IP appears on one, many mail servers will reject or spam-filter your emails automatically.

Check blocklists using MXToolbox’s blacklist lookup. If you’re listed, identify the root cause (usually one of the issues above), fix it, then request removal from the blocklist. Don’t resume high-volume sending until you’ve addressed the underlying problem, or you’ll end up right back on the list.

How to stop your emails from going to spam long term

Fixing spam issues once isn’t enough. Deliverability requires ongoing maintenance, and the habits below help you stay out of spam over time.

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  Verify new contacts before adding them to campaigns. This catches invalid addresses before they cause bounces.

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  Remove unengaged contacts after a set number of ignored emails. Continuing to email people who never open hurts your reputation.

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  Monitor domain reputation weekly using Google Postmaster Tools, or use lemlist’s Monitoring & Alerts to see warmup health, bounce trends, and inbox placement across every mailbox and domain in one view.

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  Keep sending volume steady and predictable. Spikes look suspicious to filters.

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  Use separate domains for cold outreach and transactional email. Your main company domain handles customer communication, password resets, and invoices. Protecting it from cold outreach risk is worth the small cost of a secondary sending domain.

How to recover a domain that is already flagged as spam

If your domain reputation is already damaged, recovery takes time. There’s no instant fix, but the process is straightforward.

First, stop all sends immediately. Continuing to send while flagged makes the problem worse. Second, audit your authentication records and content for any issues. Third, check blocklists and request removal where possible. Fourth, warm up again slowly: start with very low volume to engaged recipients only.

If reputation is severely damaged, consider starting fresh with a new sending domain while you rehabilitate the old one. Some domains recover in two to four weeks. Others take longer depending on how badly the reputation was damaged.

For the full repair process, tool by tool, see how to check and repair your domain reputation.

The fastest way to fix deliverability across your outbound

Managing authentication, warmup, reputation monitoring, and inbox rotation manually across multiple mailboxes is time-consuming. Most teams running outbound at scale use multiple sending domains and dozens of inboxes, which makes manual management impractical.

lemlist’s Deliverability Hub centralizes this work. You can connect existing domains or purchase new sending domains directly in the platform, with authentication configured automatically. lemwarm handles warmup. The hub monitors inbox health, flags issues early, and provides per-mailbox audits so you can catch problems before they hurt your reply rates. It’s why 20,000+ sales teams run their outbound deliverability through lemlist.

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Final thoughts

Most deliverability problems come down to a handful of fixable causes. Authentication gaps, reputation damage, dirty lists, missing warmup. The diagnostic logic is always the same: check your authentication first, then your reputation, then your content and sending patterns. Work through them in order, and you’ll find the issue.

If you’re managing more than a couple of inboxes, doing this manually gets old fast. lemlist’s Deliverability Hub, warmup, and monitoring tools handle the plumbing so you can focus on writing emails people actually want to read.

Start a 14-day free trial

No credit card required. Cancel anytime.