Why Your Klaviyo Emails Are Going to Spam (And How to Fix It)

Everyone knows spam trigger words are bad. Nobody sending ecommerce email in 2026 is dropping “FREE MONEY!!!” into their subject lines. The advice is decades old and the problem has largely been solved, by filters that stopped caring about keyword lists and started caring almost exclusively about engagement signals. Yet brands still land in spam every week. The causes are more interesting than trigger words, and fixing them requires a different diagnosis.

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The Real Reasons Emails Go to Spam

Low Engagement History

Gmail’s spam filters are engagement-first. If your contacts historically don’t open your emails, Gmail starts routing your messages to spam before they even have a chance to ignore them. This is a self-reinforcing cycle: spam placement reduces opens, reduced opens hurt reputation, hurt reputation causes more spam placement.

The threshold at which Gmail starts filtering is not public, but from observing hundreds of accounts: when fewer than 20% of your Gmail recipients have opened an email in the last 90 days, you’re at high risk of progressive spam filtering. Gmail doesn’t flip a switch. It starts routing borderline cases to spam, which gradually expands as engagement continues to fall.

Sending to Too Many Disengaged Contacts

The single most common cause of spam placement for Klaviyo accounts is a large, unmaintained list with thousands of contacts who haven’t engaged in 6–12 months. These contacts don’t just fail to help your deliverability. They actively harm it. Every email sent to someone who doesn’t open is a negative engagement signal, and negative engagement signals from Gmail users compound into domain reputation damage.

The counterintuitive truth: a list of 15,000 engaged contacts will outperform a list of 80,000 mixed contacts every time, on deliverability, on revenue per email, and on ROI.

Sudden Send Volume Increases

If you normally send to 10,000 contacts and you blast 75,000 for a Black Friday campaign, mailbox providers treat that volume spike as suspicious. Reputation is built at specific send volumes. Dramatically exceeding your normal volume tells spam filters that something unusual is happening, which triggers more aggressive filtering.

This is especially relevant for BFCM. Brands that haven’t sent consistently for 6–8 weeks leading into November, then suddenly spike volume, see the worst deliverability outcomes of the year.

Technical Authentication Gaps

DMARC policy gaps are still causing spam placement in 2026. If your domain doesn’t have a DMARC record at all, or has one set to p=none with no monitoring, you’re leaving the door open for spoofing and giving mailbox providers less confidence in your mail. Fully DMARC-authenticated domains are 2.7× more likely to reach the inbox, yet only 18.2% of the top 10 million domains have a valid DMARC record. Since Google and Yahoo’s February 2024 enforcement, domains without proper DMARC records are increasingly filtered or rejected.

Check your DMARC status at dmarcian.com or mxtoolbox.com. In Klaviyo, go to Settings > Domains and verify all three: SPF passing, DKIM signing enabled, DMARC record present.

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Spam Trigger Words vs. Engagement Signals: What Actually Matters

Modern spam filters run machine learning models, not keyword blocklists. Subject line word choice is a signal, but it’s a weak one compared to:

• Recipient engagement rate: has this contact opened your last 5 emails?
• Complaint history: has anyone from this domain hit “mark as spam” on your mail before?
• Domain reputation score: visible in Google Postmaster Tools
• Authentication pass/fail: is SPF and DKIM passing consistently?

This doesn’t mean copy is irrelevant. All-caps subject lines, excessive punctuation, certain financial terms in high density, and promotional phrases in specific combinations can still contribute to filter scores. But if a brand’s engagement rate is strong and authentication is clean, copy variations rarely cause spam placement alone.

Where copy genuinely matters: unsubscribe clarity. If your unsubscribe link is buried, slow to process, or requires a login to complete, complaint rates go up. Gmail’s complaint threshold for reputation damage is 0.08%. At 0.10%, Gmail’s documentation states they begin actively filtering your mail. Senders who implement one-click unsubscribe consistently record complaint rates below 0.1%, well clear of Gmail’s enforcement threshold. In Klaviyo, unsubscribes process immediately. But if you’re using a custom preference centre or footer, verify the unsubscribe path works in under 2 clicks.

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How Segmentation Directly Impacts Deliverability

Sending the right email to the right person is not just a revenue optimisation. It’s a deliverability strategy. Here’s why: Gmail’s inbox placement decision is partially individualised. A contact who always opens your emails is more likely to see your next email in the inbox, regardless of your domain reputation. A contact who never opens shifts their inbox placement toward spam over time.

This means your most important deliverability segment is your engaged segment. In Klaviyo, define it as:

• Opened or clicked email in the last 90 days
• OR placed an order in the last 90 days

Send every campaign to this segment by default. Layer in the 90–180 day segment for important sends. Reserve the full list (including 180+ day contacts) only for re-engagement campaigns, never for regular broadcasts.

Klaviyo setup: Create a segment with condition “Properties about someone > What someone has done > Opened Email > at least once > in the last 90 days.” Use this as the recipient list for regular campaigns. You’ll reduce your raw send numbers but improve inbox placement, engagement metrics, and ultimately revenue per campaign.

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How to Diagnose Spam Placement in Klaviyo

Klaviyo’s native reporting doesn’t directly tell you when you’re in spam. You have to infer it or test for it.

Inference signals to watch:

• Open rate dropping 20%+ over 30 days without a change in send frequency or list composition
• Click-to-open rate (CTOR) falling even as total opens stay flat. This often indicates machine-opened emails being counted as opens while real humans aren’t seeing your mail
• Gmail open rate significantly lower than other providers. Gmail’s average inbox placement (87.2%) is significantly better than Outlook’s (75.6%), so the gap between your Gmail and Outlook open rates is a useful diagnostic. If your Outlook open rate is 28% and your Gmail open rate is 9%, Gmail is filtering you

Direct testing:

• Use GlockApps (paid) or Mail Tester (free, limited) to test inbox placement before major sends
• Create a seed list of personal Gmail, Outlook, Yahoo, and Apple Mail addresses and send to them before launching large campaigns
• Connect Google Postmaster Tools (Settings > Integrations in Klaviyo) to see your domain reputation score directly from Google. “High” is good, “Medium” means you’re close to a problem, “Low” means you’re being actively filtered

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The Fix Checklist: In Priority Order

Immediate actions:

• Verify SPF, DKIM, DMARC via mxtoolbox.com or Klaviyo’s domain settings
• Connect Google Postmaster Tools to Klaviyo and check domain reputation
• Pull your complaint rate in Klaviyo’s deliverability hub. If above 0.05%, stop all broad sends
• Identify your 30-day engaged segment and switch all campaigns to it immediately

Within 2 weeks:

• Build a suppression segment: anyone who hasn’t opened or clicked in 180+ days and has never purchased → suppress in Klaviyo
• Audit your unsubscribe flow. Test it from a real inbox and time how long it takes to process
• Check whether your campaigns have Smart Sending enabled (Klaviyo’s default 16-hour skip window)

Within 30 days:

• Run a seed list test before your next major campaign
• Set up a sunset flow to automatically identify and suppress contacts after 90 days of inactivity (see the list cleaning guide for the exact setup)
• Review your DMARC policy. If you’re on p=none, plan the transition to p=quarantine once you’ve confirmed legitimate mail is passing cleanly

Ongoing:

• Monitor Google Postmaster Tools weekly
• After every campaign send, check bounce rate (flag anything above 0.5%) and complaint rate (flag anything above 0.05%). Keeping bounce rates under 1.5% is associated with 10–12% higher inbox placement
• Treat your engaged segment as the default audience for all non-reactivation sends

Most spam placement problems are fixable in 4–8 weeks with the right send discipline. The goal isn’t to trick filters. It’s to send mail that recipients actually want, which is exactly what inbox algorithms reward.

Need a deliverability audit? Book a free review.

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Sources

• MailReach, 2025 Email Deliverability Statistics