Deliverability Tools That Work with Klaviyo

Your open rates dropped from 28% to 19% over the last two months. You haven't changed anything. Same content, same audience, same send times. So what happened?

Deliverability happened. Your emails started landing in spam or the promotions tab instead of the primary inbox, and Klaviyo's built-in analytics can't tell you why. All Klaviyo shows you is that fewer people opened. It doesn't show you where those emails actually ended up.

This is the deliverability blind spot. Klaviyo is excellent at sending emails and tracking engagement. But it's not a deliverability monitoring tool. It doesn't tell you whether Gmail is sending you to spam. It doesn't alert you when your domain reputation drops. It doesn't show you which ISPs are blocking you.

For that, you need external tools. Here are the ones that actually work, what they do, and how to use them alongside Klaviyo to keep your emails in the inbox.

Understanding the Deliverability Stack

Email deliverability depends on three layers:

Layer 1: Infrastructure. Your sending domain, IP reputation, authentication records (SPF, DKIM, DMARC). These are the technical foundations that ISPs check before they even look at your email content.

Layer 2: Reputation. Your sender reputation score, which ISPs calculate based on engagement rates, spam complaint rates, bounce rates, and spam trap hits. This changes over time based on your sending behavior.

Layer 3: Content. The actual email content, including text, images, links, and HTML structure. Spam filters evaluate content for patterns associated with spam.

Most deliverability problems start at layer 1 or 2. Content issues are less common but harder to diagnose. The tools below address each layer.

Tool 1: Google Postmaster Tools (Free)

What it does: Shows you how Gmail specifically handles your emails. Includes domain reputation, IP reputation, spam rate, authentication status, and encryption metrics.

Why you need it: Gmail is typically 30-50% of any eCommerce email list. If Gmail is throttling or spam-filtering your emails, you're losing a massive chunk of your audience. Google Postmaster is the only direct source of truth for how Gmail perceives your sending reputation.

Setup: Go to postmaster.google.com. Verify ownership of your sending domain (the domain in your "From" address). Google will ask you to add a DNS record for verification. Once verified, data starts flowing within 24-48 hours.

What to watch:

• Domain reputation: Should be "High." If it drops to "Medium" or "Low," you have a problem.
• Spam rate: Should be below 0.1%. Above 0.3% is a red flag.
• Authentication: SPF, DKIM, and DMARC should all show green (passing).

How to use with Klaviyo: If Google Postmaster shows declining reputation, look at your Klaviyo metrics for the same time period. Did you send to a new segment? Import a list? Get higher-than-normal spam complaints? The Klaviyo data tells you what you did; Postmaster tells you how it affected your Gmail deliverability.

Tool 2: MXToolbox (Free + Paid)

What it does: Checks your domain and IP against 100+ blacklists, verifies DNS records (SPF, DKIM, DMARC), and monitors your sending infrastructure for issues.

Why you need it: If your sending IP or domain gets listed on a blacklist, multiple ISPs will reject or spam-filter your emails. MXToolbox is the fastest way to check if you're blacklisted and to monitor for new listings.

Setup: Go to mxtoolbox.com. Run a "Blacklist Check" on your sending domain. Run a "DNS Check" to verify your SPF, DKIM, and DMARC records are properly configured.

What to watch:

• Blacklist status: Should be clear on all major lists. If you're listed anywhere, investigate immediately.
• SPF record: Should include Klaviyo's sending servers.
• DKIM: Should be properly configured with Klaviyo's signing domain.
• DMARC: Should have a policy set (at minimum, p=none for monitoring).

How to use with Klaviyo: Klaviyo provides the SPF and DKIM records you need to add to your DNS when you set up a dedicated sending domain. Use MXToolbox to verify those records are correctly published and propagated.

Tool 3: GlockApps (Paid — Starting at $59/month)

What it does: Sends seed emails to test inboxes at every major ISP (Gmail, Yahoo, Outlook, etc.) and tells you exactly where your email landed — inbox, spam, promotions tab, or missing entirely.

Why you need it: This is the only way to know for certain whether your emails are hitting the inbox at each ISP. Klaviyo can't tell you this. Open rates are an imperfect proxy because tracking pixel blocking means some opens go unrecorded.

Setup: Create a GlockApps account. They provide you with a list of seed email addresses. Add these addresses to a test segment in Klaviyo. Before every major campaign or when troubleshooting, send to this seed list first.

What to watch:

• Inbox placement rate by ISP (target 90%+ for major ISPs)
• Spam placement rate (should be 0% or near-zero)
• Missing emails (indicates blocking, not just spam filtering)
• Promotions tab placement (Gmail-specific, not ideal but not spam)

How to use with Klaviyo: Add GlockApps seed addresses to a dedicated "Deliverability Testing" list in Klaviyo. Before launching a campaign to your full list, send it to the seed list first. If GlockApps shows spam placement at any major ISP, don't send the full campaign until you've identified and fixed the issue.

Tool 4: Mail Tester (Free — Limited Checks)

What it does: Scores your email on a 1-10 scale based on technical factors: authentication, content quality, blacklist status, HTML quality, and server configuration.

Why you need it: It's the quickest, simplest gut-check for email quality. Send a test email to the Mail Tester address, get an instant score, and see exactly what's wrong.

Setup: Go to mail-tester.com. They show you a unique email address. Send your Klaviyo test email to that address. Refresh the page to see your score.

What to watch:

• Overall score: Target 9/10 or higher.
• Authentication: SPF, DKIM, and DMARC should all pass.
• Content: No spam trigger words, good text-to-image ratio.
• Blacklists: No listings.
• HTML quality: No broken links, proper formatting.

How to use with Klaviyo: Run every new email template through Mail Tester before adding it to your flow or campaign. If the score is below 8, fix the flagged issues before sending.

Tool 5: Validity (formerly Return Path) — Enterprise

What it does: Comprehensive inbox monitoring, reputation tracking, and deliverability analytics across all major ISPs. Includes real-time alerting when reputation drops or inbox placement changes.

Why you need it: For brands sending 500K+ emails per month, the enterprise-level monitoring is worth the investment. Validity provides the most granular inbox placement data and reputation scoring available.

When to consider: If your email revenue exceeds $100K/month and you're sending to 100K+ subscribers, the ROI on Validity's monitoring ($500-2,000/month depending on volume) is justified by the revenue protection it provides.

Setting Up Your Deliverability Monitoring Stack

For most eCommerce brands on Klaviyo, here's the recommended stack by size:

Under 50K subscribers (Starter):

• Google Postmaster Tools (free) — Gmail monitoring
• MXToolbox (free) — DNS and blacklist checks
• Mail Tester (free) — Email quality scoring

Total cost: $0/month

50K-200K subscribers (Growth):

• Everything above, plus:
• GlockApps ($59-79/month) — Inbox placement testing

Total cost: $59-79/month

200K+ subscribers (Scale):

• Everything above, plus:
• Validity or InboxMonitor — Real-time reputation monitoring and alerting

Total cost: $200-500+/month

The Monthly Deliverability Audit

Regardless of which tools you use, run this check monthly:

Week 1: Check Google Postmaster Tools. Review domain reputation, spam rate, and authentication status. Note any changes from last month.

Week 2: Run a blacklist check on MXToolbox. Verify SPF, DKIM, and DMARC records are still correctly configured (they can break if someone changes DNS records without realizing the impact).

Week 3: Send a seed test through GlockApps (if you have it). Check inbox placement across ISPs. Compare to last month's results.

Week 4: Review Klaviyo metrics. Compare open rates, click rates, bounce rates, and spam complaint rates to the previous month. Correlate any declines with what you found in the external tools.

If all four checkpoints come back clean, your deliverability is healthy. If any show decline, you have a diagnostic trail to identify the root cause.

Common Deliverability Problems and Fixes

Problem: Gmail reputation dropped to "Medium." Cause: Usually triggered by spam complaints exceeding 0.1% or engagement rates dropping significantly. Fix: Tighten your send segment. Only email people who've opened or clicked in the last 60-90 days for 2-4 weeks. Your engagement rates will spike, repairing the reputation.

Problem: Listed on a minor blacklist. Cause: A spam trap hit, usually from an old list import or a purchased list. Fix: Request delisting from the blacklist (most have a delisting form). Then audit your list for inactive addresses that might be recycled spam traps. Run a list cleaning service like ZeroBounce or NeverBounce.

Problem: High promotions tab placement in Gmail. Cause: Your email looks too "promotional" — heavy design, lots of images, minimal text, multiple links. Fix: Increase your text-to-image ratio. Send more plain text emails. Reduce the number of links per email. Encourage replies.

Problem: Emails missing (not in inbox or spam). Cause: Your emails are being blocked at the server level, not just filtered. This is severe — the ISP is rejecting your emails entirely. Fix: Contact the ISP's postmaster (most have a form). Provide your sending domain and IP. This usually requires working with Klaviyo support to address infrastructure issues.

Deliverability is invisible until it breaks. These tools make the invisible visible so you can catch problems before they eat your revenue.

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