You wrote the perfect email. Great subject line, compelling content, clear call to action. But your recipient never sees it because Gmail quietly dropped it into their spam folder.
This happens more often than you'd think. Even legitimate, well-intentioned emails get flagged as spam. And unlike a bounced email, you don't get a notification — your email just disappears into a folder that most people never check.
The good news: spam filtering isn't random. There are specific, fixable reasons why emails land in spam. In this guide, we'll walk through the most common causes and exactly how to fix each one.
How Gmail's Spam Filter Works
Gmail uses a multi-layered approach to filter spam. Understanding the basics helps you avoid triggering it:
Sender reputation
Every email-sending domain and IP address has a reputation score. Gmail tracks how recipients interact with emails from your domain. If people frequently mark your emails as spam, delete them without reading, or never engage with them, your reputation drops.
A bad sender reputation means even perfectly crafted emails will get flagged. A good reputation means Gmail gives your emails the benefit of the doubt.
Authentication checks
Gmail checks whether the email actually came from who it claims to be. This is done through three protocols: SPF, DKIM, and DMARC. If any of these are misconfigured or missing, Gmail is more likely to flag your emails.
Content analysis
Gmail scans the email content for spam-like patterns: excessive links, suspicious attachments, known spam phrases, mismatched formatting, and more. This is the layer most people are familiar with.
User behavior signals
If the specific recipient has marked previous emails from you (or from similar senders) as spam, Gmail learns that preference. This is personalized — your email might land in one person's inbox and another's spam folder.
The Technical Foundation: SPF, DKIM, and DMARC
If you're sending from a custom domain (anything other than @gmail.com), these three DNS records are essential. Without them, you're essentially sending emails without ID.
SPF (Sender Policy Framework)
SPF tells email servers which IP addresses are authorized to send email on behalf of your domain. It's a DNS TXT record that lists your legitimate sending sources.
What to do: Add an SPF record to your domain's DNS settings. If you're using Google Workspace, it looks like this:
v=spf1 include:_spf.google.com ~all
If you also use other email services (Mailchimp, SendGrid, etc.), add their includes too. You can only have one SPF record per domain.
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your emails that proves they haven't been tampered with in transit. It's like a wax seal on a letter — if the seal is broken, the recipient knows something's wrong.
What to do: Enable DKIM in your Google Workspace admin console (Admin > Apps > Google Workspace > Gmail > Authenticate Email). Google generates a TXT record that you add to your DNS.
DMARC (Domain-based Message Authentication)
DMARC ties SPF and DKIM together and tells receiving servers what to do if an email fails authentication checks. It also enables reporting, so you can see who's sending emails claiming to be from your domain.
What to do: Start with a monitoring-only DMARC record:
v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com
This collects reports without blocking any emails. Once you're confident your authentication is set up correctly, change p=none to p=quarantine or p=reject.
How to check your setup
Send a test email to a Gmail address and open it. Click the three dots menu in Gmail and select "Show original." Look for these headers:
- SPF: PASS
- DKIM: PASS
- DMARC: PASS
If any of these show FAIL or NEUTRAL, that's what needs fixing.
Content Mistakes That Trigger Spam Filters
Even with perfect authentication, your email content can trip spam filters. Here are the most common triggers:
1. Spam trigger words
Certain words and phrases make spam filters suspicious, especially in subject lines:
- "FREE!!!" or excessive capitalization
- "Act now" / "Limited time" / "Urgent"
- "Click here" (as the sole link text)
- "Congratulations, you've been selected"
- "No obligation" / "Risk-free" / "100% guaranteed"
- Money-related: "$$$" / "Earn extra cash" / "Double your income"
This doesn't mean you can never use these words. Context matters. "Free trial" in a legitimate SaaS email is fine. "FREE MONEY ACT NOW" in all caps is obviously spam. Use common sense and write like a human, not a late-night infomercial.
2. Image-heavy emails with little text
Emails that are mostly images with minimal text look suspicious to spam filters. Spammers historically put their message in an image to bypass text-based filters. If your email is one giant image, add meaningful text around it.
A good rule of thumb: at least 60% text, no more than 40% images.
3. Too many links
An email with 15 links in it looks like spam. Keep links to a reasonable number — 2-5 for a business email is plenty. And make sure every link points to a legitimate, working URL.
4. Suspicious attachments
Certain file types (.exe, .zip, .js) are almost always flagged. Even PDFs and Office documents can trigger filters if they contain macros. When possible, link to files hosted on Google Drive, Dropbox, or your website instead of attaching them directly.
5. Misleading sender information
If your "From" name says "Google Support" but your email is from a random domain, that's a red flag. Make sure your sender name and email address are consistent and honest.
6. Missing unsubscribe link (bulk emails)
If you're sending to a list, every email must include an unsubscribe link. Gmail requires this, and missing it is a fast path to the spam folder. For one-to-one tracked emails through Trackable, this doesn't apply.
Behavioral Factors That Hurt Deliverability
Low engagement rates
If you send 100 emails and only 5 people open them, Gmail notices. Low open rates signal that recipients don't want your emails, which hurts your sender reputation. This is why list hygiene matters — remove inactive subscribers regularly.
High bounce rate
Sending to invalid email addresses generates bounces. A high bounce rate tells Gmail you're not maintaining your list, which is a spam behavior signal. Verify email addresses before sending, especially for cold outreach.
Spam complaints
Even a small percentage of recipients clicking "Report spam" can tank your deliverability. The industry threshold is 0.1% — if more than 1 in 1,000 recipients report your email as spam, Gmail starts filtering your messages.
Sending volume spikes
If you normally send 20 emails a day and suddenly send 500, Gmail flags this as suspicious. Warm up gradually. If you're starting a new email campaign, increase volume by 20-30% per day, not 10x overnight.
Gmail-Specific Tips
Use Google Postmaster Tools
Google Postmaster Tools (postmaster.google.com) is free and shows you exactly how Gmail views your domain. You can see your domain reputation, spam rate, authentication results, and delivery errors. Set it up if you haven't already.
Warm up a new domain
Brand new domains have no reputation, which means Gmail is cautious. For the first few weeks, send small volumes to people who are likely to engage (colleagues, friends, warm contacts). Build a positive engagement history before scaling up.
Use a consistent sending pattern
Gmail's algorithms look for consistency. Sending the same type of email at roughly the same time and volume is a positive signal. Erratic patterns (nothing for weeks, then a blast of 200 emails) look spammy.
Encourage replies
Emails that receive replies have the strongest positive signal. Gmail sees that the recipient engaged in a conversation, which reinforces that your emails are wanted. Write emails that invite responses — ask questions, request feedback, start conversations.
How to Tell If Your Emails Are Going to Spam
The trickiest part about spam folder issues is that you often don't know it's happening. Here are ways to detect it:
- Track your open rates — A sudden drop in open rates is the clearest signal. Use Trackable to monitor your email opens. If emails that should be opened aren't, spam filtering might be the cause.
- Send test emails — Send to your own Gmail, Outlook, and Yahoo addresses. Check both inbox and spam folder.
- Check Google Postmaster Tools — Look at your spam rate and domain reputation over time.
- Ask recipients — If someone isn't responding, consider reaching out through another channel to ask if they received your email.
Quick Checklist: Before You Hit Send
- SPF, DKIM, and DMARC are configured and passing
- Subject line avoids spam trigger words and ALL CAPS
- Email has a healthy text-to-image ratio
- Links are reasonable in number and point to legitimate URLs
- No suspicious attachments
- Sender name and email are consistent and trustworthy
- You're sending to valid, engaged email addresses
- Your sending volume is consistent (no sudden spikes)
- Bulk emails include an unsubscribe link
Frequently Asked Questions
My emails were fine before but suddenly go to spam. What happened?
Most likely: your domain reputation dropped (check Google Postmaster Tools), someone on your list reported you as spam, or your authentication records were changed or expired during a DNS update. Check each factor systematically.
Does email tracking affect spam deliverability?
No. Modern email trackers like Trackable use tracking pixels that are standard HTML images — the same technology used by every email marketing platform. Gmail doesn't penalize emails for containing tracking pixels. The tracking pixel is tiny and invisible, adding negligible weight to the email.
Should I use a subdomain for bulk emails?
Yes. If you send both personal emails and marketing campaigns from the same domain, a spam issue with your campaigns can affect your personal email deliverability. Use a subdomain (like mail.yourdomain.com) for bulk sending to isolate reputation.
Can I get removed from spam once I'm flagged?
Yes, but it takes time. Fix the root cause (authentication, content, list quality), then slowly rebuild your reputation by sending small volumes to engaged recipients. Improvements in Google Postmaster Tools typically show within 2-4 weeks.