Email Deliverability Monitoring Tools Compared (2026)

Free Monitoring Tools

Start here. These tools cost nothing and provide essential data.

Google Postmaster Tools

What it monitors: Domain and IP reputation for Gmail, spam rate, authentication pass rates, delivery errors.

Best for: Anyone sending to Gmail (most lists are 30-50% Gmail).

Setup: Verify domain ownership, wait for data (requires volume).

Limitations: Gmail only. No inbox vs promotions distinction. Requires 100+ daily emails to show data.

See our complete Google Postmaster Tools guide.

Microsoft SNDS (Smart Network Data Services)

What it monitors: IP reputation, spam trap hits, complaint rates for Outlook/Hotmail.

Best for: B2B senders (Outlook-heavy audiences), enterprise email.

Setup: Verify IP ownership or request access.

Limitations: IP-based only (not domain), requires dedicated IP.

See our Microsoft SNDS setup guide.

Mail-Tester

What it monitors: Authentication, content spam score, blacklists, HTML quality.

Best for: Pre-send content checks, one-off troubleshooting.

Setup: Send test email to their unique address.

Limitations: 3 free tests/day. Point-in-time only, not continuous monitoring.

Cost: Free (limited), $24/month for more tests.

MXToolbox

What it monitors: Blacklists, DNS records, SMTP diagnostics.

Best for: Quick blacklist checks, DNS verification.

Setup: Enter domain or IP.

Limitations: Basic checks only. Blacklist monitoring requires paid plan ($99+/month).

Paid Monitoring Tools

GlockApps

What it monitors: Inbox placement by provider, spam folder rates, authentication, content analysis, blacklists.

Best for: Regular inbox placement testing, pre-campaign checks.

Pricing:

• Personal: $59/month (6,000 tests/month)
• Business: $99/month (12,000 tests/month)
• Agency: $199/month (30,000 tests/month)

Strengths:

• Real inbox testing (not simulated)
• Provider-by-provider breakdown
• DMARC monitoring included
• Content spam analysis

Weaknesses:

• Test results are point-in-time
• Seed list doesn't perfectly match real audiences
• Some UI clunkiness

Practitioner note: GlockApps is my go-to recommendation for mid-market senders. The $59/month plan provides enough tests to check before every major campaign and diagnose issues quickly. The inbox placement data is actionable.

Validity Everest (formerly Return Path)

What it monitors: Inbox placement, reputation, certification status, competitive intelligence.

Best for: Enterprise senders, agencies managing multiple domains, deliverability professionals.

Pricing: $1,000-5,000+/month (custom quotes)

Strengths:

• Deepest reputation data available
• Inbox Preview for rendering tests
• Certification program access
• Competitive benchmarking
• Dedicated support

Weaknesses:

• Expensive for SMBs
• Complex setup
• Some features require additional cost

Verdict: If you have a dedicated deliverability person or team, Everest is the gold standard. For most businesses, it's overkill.

InboxReady (by Sinch/Mailgun)

What it monitors: Inbox placement, reputation, content analysis.

Best for: Mailgun users, companies wanting integrated monitoring.

Pricing: Included with some Mailgun plans, standalone ~$200-500/month.

Strengths:

• Tight Mailgun integration
• Real-time alerts
• Clean interface

Weaknesses:

• Newer product, less track record
• Less comprehensive than Validity

Warmy.io

What it monitors: Warmup progress, inbox placement, reputation.

Best for: Cold emailers doing warmup who want monitoring bundled.

Pricing: $49-99/month (warmup + monitoring)

Strengths:

• Combines warmup and monitoring
• Good for cold email use case

Weaknesses:

• Less strong than dedicated tools
• Focused on warmup, monitoring is secondary

Tool Comparison Matrix

Tool	Inbox Testing	Reputation	Blacklist	Content	Price
Google Postmaster	No	Gmail only	No	No	Free
Microsoft SNDS	No	Outlook only	No	No	Free
Mail-Tester	Limited	No	Yes	Yes	Free-$24/mo
GlockApps	Yes	Basic	Yes	Yes	$59-199/mo
Validity Everest	Yes	Deep	Yes	Yes	$1,000+/mo
InboxReady	Yes	Yes	Yes	Yes	$200-500/mo

Building a Monitoring Stack

For Small Senders (<25K/month)

Free stack:

1. Google Postmaster Tools (Gmail reputation)
2. Microsoft SNDS (if using dedicated IP)
3. Mail-Tester (pre-campaign checks)
4. ESP bounce and complaint dashboards

Cost: $0

For Mid-Market Senders (25K-500K/month)

Recommended stack:

1. Google Postmaster Tools
2. GlockApps Business ($99/month)
3. Blacklist monitoring (MXToolbox or GlockApps)
4. ESP analytics

Cost: ~$100/month

For Enterprise Senders (500K+/month)

Full stack:

1. Validity Everest
2. Google Postmaster Tools
3. Custom seed lists
4. Real-time alerting integration

Cost: $1,500+/month

Practitioner note: The jump from GlockApps to Validity Everest is steep—both in price and complexity. Unless you have someone dedicated to deliverability, you won't extract full value from enterprise tools.

What to Monitor and When

Daily

• Bounce rates in ESP
• Spam complaint rates
• Delivery success rates

Weekly

• Google Postmaster reputation
• Microsoft SNDS data
• Blacklist checks

Before Major Campaigns

• GlockApps inbox placement test
• Mail-Tester content check
• Authentication verification

After Any Issue

• Run immediate inbox placement test
• Check all reputation tools
• Monitor daily until resolved

When to Upgrade Your Tools

Consider paid monitoring when:

• You've experienced a deliverability crisis
• You're sending 50K+ emails monthly
• Gmail or Outlook placement has declined
• You're migrating ESPs or IPs
• You manage multiple sending domains

If you're unsure which tools fit your situation or need help interpreting the data they provide, schedule a consultation to build a monitoring stack matched to your sending volume and goals.

Sources

• Google: Postmaster Tools
• Microsoft: SNDS
• GlockApps: Pricing
• Validity: Everest

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v1.0 · March 2026