Most teams check their deliverability once — usually after something breaks. By then the damage is already showing up in reply rates. Fifteen minutes with the right free tools before every campaign launch would catch 90% of deliverability problems before they cost you anything. Here are the seven tools worth using and exactly how to run them.
TL;DR
💡 TL;DR
The only non-negotiable free deliverability check is Google Postmaster Tools — it's the only tool that measures what actually drives Gmail inbox placement. Use MXToolbox for DNS verification, Mail-tester.com for a quick end-to-end score, and Microsoft SNDS for Outlook reputation. Run all four before every campaign launch and after every inbox infrastructure change. Litemail pre-warmed inboxes consistently score 10/10 on mail-tester.com and show Good or High in Postmaster Tools within 48 hours of delivery.
The 7 Free Tools (and What Each One Actually Measures)
These aren't ranked by quality — they measure different things. You need all of them because each one catches a different class of problem.
1. Google Postmaster Tools (postmaster.google.com)
The most important tool on this list. Free, provided by Google. Shows domain reputation, IP reputation, spam rate, authentication pass rate, and delivery errors for your sending domains with Gmail.
What it catches: Poor domain reputation from complaint history, IP reputation problems, authentication failures at scale, and delivery error patterns. What it misses: Outlook/Hotmail placement, content-level filtering, and blacklist status.
How to use it: Add your sending domain, wait 24–48 hours after the first send, then check Domain Reputation. Good or High = proceed. Medium = wait and recheck. Low or Unknown = stop and investigate before sending any campaigns.
2. MXToolbox (mxtoolbox.com)
Free DNS diagnostic tool. Checks SPF, DKIM, and DMARC configuration, blacklist status across 100+ blacklists, and MX record setup. Run this before any other check — if DNS is broken, nothing else matters.
How to use it: Enter your sending domain → run Email Health Check. All three DNS records should show green. Any red means fix before proceeding.
3. Mail-tester.com
Free inbox placement test. Gives you a score out of 10 based on a test email sent to their unique address. Checks SPF/DKIM/DMARC pass, spam score, blacklist status, and several content signals.
What it catches: Configuration errors, spam content triggers, and basic blacklist presence. What it misses: Actual Gmail placement (its score doesn't directly correlate to Postmaster reputation). A 10/10 on mail-tester doesn't guarantee Good Postmaster reputation.
Target score: 9/10 or 10/10. A Litemail pre-warmed inbox consistently scores 10/10. Below 8/10 means configuration or content problems to fix.
4. Microsoft SNDS (postmaster.live.com)
Microsoft's equivalent of Postmaster Tools. Shows IP reputation with Microsoft mail servers (Outlook, Hotmail, Exchange). Free, requires registration with your sending IP addresses.
What it catches: IP reputation problems with Microsoft's infrastructure, junk mail complaint rates from Outlook users. Critical for any team targeting enterprise prospects who use MS365.
5. Sender Score (senderscore.org — now part of Validity)
IP reputation score from 0–100. Shows how your sending IP is rated by Validity's network. A score below 70 indicates reputation problems that are actively hurting deliverability.
What it catches: IP-level reputation problems across Validity's network (covers many ISPs and enterprise mail servers). What it misses: Domain-level reputation (use Postmaster Tools for that).
6. Blacklist Check via MXToolbox or MXBlacklist.com
Check whether your sending domain or IP is on any major blacklist. Run this before every campaign and after any period of elevated complaint rates.
What it catches: Active blacklist presence on Spamhaus, Barracuda, SORBS, and 100+ others. What it misses: Greylist status and internal ISP reputation systems.
7. GlockApps or Mailtrap Inbox Placement Test (limited free tier)
Seed list test — sends your email to test addresses across Gmail, Outlook, Yahoo, and other providers and shows exactly where it landed (primary inbox, spam, or missing). GlockApps has a limited free plan; Mailtrap has a free trial.
What it catches: Actual placement across multiple email providers simultaneously — the most realistic deliverability picture. What it misses: Nothing significant, though results can vary slightly from real campaign sends.
The 15-Minute Pre-Campaign Deliverability Checklist
Run these in order. Each step takes 2–4 minutes. Together they cover every common deliverability problem before you send a single campaign email.
MXToolbox DNS check (3 min): Check SPF, DKIM, DMARC. All three green? Proceed. Any red? Fix before continuing.
Mail-tester.com score (3 min): Send test email, check score. 9–10/10? Proceed. Below 8/10? Check the failure items.
Google Postmaster Tools (2 min): Check domain reputation for every sending domain. Good or High? Proceed. Medium? Wait 48 hours and recheck.
Blacklist check via MXToolbox (2 min): Check domain and sending IP. Any active blacklists? Address before sending.
Microsoft SNDS check (2 min): Relevant if more than 30% of your prospect list uses Outlook/Exchange. Check IP reputation status — Green (clean), Yellow (elevated), or Red (blocked).
Manual test send (3 min): Send a test email from each active inbox to a Gmail address and an Outlook address you control. Check the email headers (Gmail: three dots → Show original) — SPF: PASS, DKIM: PASS, DMARC: PASS. Any FAIL? Stop and fix.
What Free Tools Miss (And When to Use Paid)
Free tools have real gaps. Here's what they can't catch, so you know when to add a paid tool to the stack.
Content-level spam filtering: Free tools catch obvious spam triggers but miss the nuanced content patterns that specific ISPs flag. Paid tools like SpamAssassin integration or Folderly's inbox placement test are more thorough for content analysis.
Per-ISP placement breakdown: GlockApps (paid) shows placement broken down by specific mail provider. Free seed tests show aggregate results. If you have specific placement problems with one provider (e.g., Yahoo only, or Hotmail only), paid per-ISP reporting identifies the specific issue.
Historical reputation trends: Postmaster Tools shows current status but doesn't give a clean historical view of reputation over time. Paid tools like EmailGuard or Inboxally track reputation trends over months — useful for identifying gradual reputation decline before it becomes critical.
For most cold email teams, the seven free tools above cover 90% of deliverability diagnostics. The paid layer is for teams sending at high volume (1,000+ emails per day) where small placement percentage differences have meaningful pipeline impact.
The Fix That Makes All These Tools Easier to Pass
Running these tools on a pre-warmed inbox versus a fresh inbox produces fundamentally different results. Not because the tools score them differently — but because pre-warmed inboxes start from a position that passes every check from day one.
In our experience at Litemail, a pre-warmed inbox at delivery passes the full 15-minute checklist on the first run: Good or High in Postmaster Tools, 10/10 on mail-tester.com, all DNS green, clean SNDS status, zero blacklists. Fresh inboxes under 30 days typically pass DNS and mail-tester but show Unknown in Postmaster Tools — which means they're not ready for campaigns yet regardless of the other checks.
The pre-campaign checklist exists to verify your setup. Pre-warmed infrastructure exists to ensure it passes.
Ongoing Monitoring: What to Check Weekly
Pre-campaign checks prevent launch mistakes. Weekly monitoring catches degradation before it becomes a campaign problem.
Monday: Postmaster Tools — Check domain reputation for all active sending domains. 5 minutes.
Monday: Complaint rate — Check spam rate in Postmaster Tools per domain. Flag anything above 0.08%.
Wednesday: Active campaign bounce rate — Flag any campaign with bounce rate above 2%.
Friday: One random mail-tester check — Pick one active inbox, send a test, confirm 9–10/10.
This weekly routine takes 20 minutes total and catches 95% of developing problems before they cause visible campaign damage. According to the 2025 Validity email deliverability benchmark, the global average inbox placement rate reached 87.2% — teams that monitor actively see significantly better than average.
Inboxes That Pass Every Deliverability Check — Try Litemail
Litemail pre-warmed inboxes consistently score 10/10 on mail-tester.com, show Good or High in Postmaster Tools within 48 hours, and pass all DNS checks on delivery. $4.99/inbox, automated DNS, dedicated US and EU IPs, full admin access. Start the 15-minute checklist with infrastructure that's designed to pass it.
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About Litemail — Litemail provides pre-warmed Google Workspace and Microsoft 365 inboxes for cold email outreach. From $4.99/inbox with automated DNS, dedicated US and EU IPs, and full admin access. View pre-warmed inbox plans →
Related reading:
SPF DKIM DMARC Auto Setup 2026 · Google Postmaster Tools Setup for Cold Email · Email Deliverability Monitoring Tools 2026 · Cold Email Deliverability Guide 2026 · Best Pre-Warmed Inbox Providers 2026 (Ranked)
Key Takeaways
Google Postmaster Tools is the non-negotiable free deliverability check — it's the only tool measuring what actually drives Gmail inbox placement.
The 15-minute pre-campaign checklist (MXToolbox → Mail-tester → Postmaster Tools → Blacklist check → SNDS → Manual test send) catches 90% of launch-blocking problems.
A 10/10 on mail-tester.com doesn't guarantee Good Postmaster reputation. Run both checks — they measure different things.
Free tools miss per-ISP placement breakdowns, content-level filtering nuances, and historical reputation trends — gaps that matter most at 1,000+ emails per day.
Weekly 20-minute monitoring (Postmaster Tools + complaint rate + bounce rate + one mail-tester check) catches 95% of developing deliverability problems before they become campaign damage.
Pre-warmed Litemail inboxes are designed to pass the full pre-campaign checklist from day one — Good/High Postmaster reputation, 10/10 mail-tester, all DNS pre-configured.
Frequently Asked Questions
What are the best free tools to check email deliverability in 2026?
Google Postmaster Tools (domain and IP reputation for Gmail), MXToolbox (DNS verification and blacklist check), Mail-tester.com (end-to-end email score), and Microsoft SNDS (IP reputation for Outlook) are the four essential free tools. Together they cover Gmail, Outlook, DNS authentication, and blacklist status — the primary deliverability factors for cold email in 2026.
How do I check if my cold email is going to spam?
Four checks: (1) Send a test email to a Gmail address and check headers (Show Original) — SPF, DKIM, and DMARC should all show PASS. (2) Check your domain in Google Postmaster Tools — Good or High reputation means Gmail is giving you inbox placement benefit of the doubt. (3) Send a test to mail-tester.com and check the score (aim for 9–10/10). (4) Run a seed list test via GlockApps free tier to see actual placement across multiple providers.
Is Google Postmaster Tools free?
Yes — completely free. Go to postmaster.google.com, sign in with a Google account, and add your sending domain. You'll see domain reputation, IP reputation, spam rate, authentication rates, and delivery errors within 24–48 hours of your first send. It's the most important free deliverability tool available and the primary way to verify pre-warmed inbox quality before campaigns.
What does a 10/10 score on mail-tester.com mean?
A 10/10 on mail-tester.com means your email passes all the checks the tool runs: SPF/DKIM/DMARC authentication, no blacklist presence, clean HTML, no obvious spam triggers, and correct sending configuration. It's a good quick check but doesn't directly measure Gmail inbox placement — that's what Postmaster Tools is for. Litemail pre-warmed inboxes consistently score 10/10 on mail-tester.com.
What is Sender Score and does it matter for cold email?
Sender Score is Validity's IP reputation score from 0–100. A score below 70 indicates IP reputation problems affecting deliverability across Validity's network of ISPs and enterprise mail servers. It measures IP-level reputation rather than domain-level — useful for diagnosing IP-specific problems but less critical than Postmaster Tools for Gmail-focused cold email. Check it monthly rather than before every campaign.
How do I know if my email domain is blacklisted?
Run an MX blacklist check at mxtoolbox.com — it checks your domain against 100+ blacklists simultaneously and shows any active listings. MXBlacklist.com is an alternative that also covers a broad blacklist database. Check both your domain and your sending IP address. If you find a blacklist entry, most blacklists have a delisting request process on their site — Spamhaus and Barracuda are the most common ones that require action.
Inboxes That Pass Every Free Check — Try Litemail
Litemail pre-warmed inboxes are designed to pass your entire pre-campaign deliverability checklist. Good or High Postmaster reputation within 48 hours, 10/10 mail-tester.com score, automated DNS pre-configured. $4.99/inbox, no minimum order. Delivered in 24 hours.
Get Pre-Warmed Inboxes from $4.99 →
10/10 mail-tester score · Verified Postmaster Good/High · Automated DNS · No minimum order
Buy Pre-Warmed Email Inboxes & Domains | Litemail
Buy pre-warmed email accounts, inboxes and domains from $4.99/inbox. Google Workspace & Microsoft 365. Automated DNS, US & EU IPs. Setup in 5 minutes.
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Related reading: Google Postmaster Tools Setup for Cold Email · Email Deliverability Monitoring Tools 2026 · SPF DKIM DMARC Auto Setup 2026 · Best Pre-Warmed Inbox Providers 2026 (Ranked) · Litemail Pre-Warmed Inboxes — Plans and Pricing
