Compare 10 email deliverability tools for inbox placement, Gmail and Outlook.com signals, DMARC, blocklists, suppression management, and pricing. Each verdict is based on current public documentation, not invented performance scores.
GlockApps is the broadest fit in this comparison for repeatable seed-based placement tests. Mailgun Optimize is stronger when validation and monitoring need to sit beside the test, while Google Postmaster Tools and Microsoft SNDS provide provider-native signals for their own ecosystems. No result from a seed list predicts every real recipient.
Email deliverability tools exist for one gap: your sending platform reports that a message was sent, but it cannot tell you whether the message landed in the inbox, the spam folder, or got filtered before delivery. When replies dry up or transactional email starts disappearing, the root cause is usually authentication that does not align (SPF, DKIM, DMARC), reputation that slipped, a spike in complaints, or a blocklist hit.
The tools below can measure the placement of test messages, surface mailbox-provider signals, and help diagnose likely causes. If you send outbound at meaningful volume, use a sending platform with warmup, pacing, and list-hygiene controls, then use provider dashboards and placement tests to monitor outcomes.
- Best for cross-provider placement tests: GlockApps, with repeatable seed tests across major mailbox providers and filter diagnostics.
- Best free provider stack: Google Postmaster Tools, Microsoft SNDS, and Yahoo Sender Hub Insights for first-party Gmail, Outlook.com, Yahoo, and AOL signals.
- Best combined vendor ecosystem: Mailgun Send plus Optimize for suppression management, validation, placement tests, and monitoring, subject to plan entitlements.
How we evaluate email deliverability tools
This comparison uses public product documentation and pricing pages checked on August 1, 2026. We assessed how each documented capability fits seven common jobs. This is not a controlled head-to-head test, and we do not assign performance scores that the published evidence cannot support.
- Inbox placement testing capability. Can it show Inbox vs Spam vs Tabs broken out by provider, or just a single generic "deliverability score"? A tool that cannot separate Gmail from Outlook from Yahoo does not provide provider-specific evidence, and filters differ by provider.
- Seed-test coverage and limits. A placement result describes the test accounts included by that vendor. We favor clear provider breakdowns and repeatable before-and-after tests, while treating the percentages as directional rather than a forecast for a real list.
- Blacklist monitoring coverage. Some tools check a handful of well-known lists; others sweep dozens, including regional and ISP-specific ones. A domain can look clean on one checker and still be blocked by a list that checker never queries.
- DMARC/SPF/DKIM diagnostics depth. The bar isn't whether a record exists, it's whether the tool catches alignment failures, for example SPF passing while the visible From domain doesn't match. Misalignment can contribute to filtering even when an individual authentication check passes. See how SPF, DKIM, and DMARC actually work together for the full mechanics.
- Warmup approach and its limits. We look for public documentation of the sending mechanism, pacing controls, and stated limitations. A warmup dashboard is not evidence of placement across a real recipient list, so we keep warmup and placement testing as separate categories.
- Pricing transparency. Can you find a current number and billing period without booking a call? When pricing is quote-based, we report that limitation instead of inferring the likely budget or value.
- API access. If verification, placement checks, or DNS lookups cannot be called programmatically, the tool lives in a dashboard someone has to remember to open, which is a workflow problem for teams sending daily.
What is an email deliverability tool (and what it isn't)?
An email deliverability tool is software that helps you inspect where test messages land (inbox vs spam), review authentication and reputation signals, and diagnose what to fix. It sits next to your sending stack and adds evidence your ESP often cannot provide on its own.
Most deliverability tools focus on four jobs: inbox placement testing (seed lists and placement reporting), authentication checks (SPF, DKIM, DMARC alignment), reputation and blocklist monitoring (domain and IP signals), and diagnostics (headers, spam filter reasons, bounce patterns).
It isn't an ESP
An email service provider like Amazon SES, Mailgun, or SendGrid sends mail and provides logs, bounces, and basic suppression. Deliverability tools add independent testing and monitoring across mailbox providers, plus clearer root-cause clues when Gmail or Outlook starts filtering you.
It isn't a cold email platform
Cold outreach platforms like Overloop, Instantly, or Apollo handle sequencing, pacing, connected sending accounts, and often list hygiene. Those controls do not make sending safe or prove inbox placement. A deliverability tool adds provider-specific measurements and diagnostics for issues such as a reputation change, DMARC misalignment, or a new Spamhaus listing.
It isn't just an email verification tool
Email verification tools like ZeroBounce, NeverBounce, or BriteVerify reduce bounces by validating addresses. That improves deliverability indirectly, but it will not tell you inbox placement, spam folder reasons, or whether Gmail sees your DKIM signature as aligned. A simple way to map the stack: your sending platform sends, your verification tool cleans the list, and your deliverability tool measures placement and reputation so you can diagnose changes before reply rates fall.
How do email deliverability tools work?
Deliverability tools work by sending test and observability signals through the same path as your real email, then translating what mailbox providers and DNS records reveal into actionable diagnoses. In practice, they answer five questions: did the message authenticate, did it reach the inbox, did it trigger filters, did a blocklist intervene, and what do reputation signals look like over time?
- Run a seed (inbox placement) test. Tools like GlockApps and Mailgun Optimize generate a seed list of real inboxes (Gmail, Outlook, Yahoo). You send your exact campaign email to those addresses, then the tool reports placement (Inbox, Spam, Tabs) and often flags the likely filter reason.
- Inspect the message and headers. Deliverability tools parse headers to check SPF pass or fail, DKIM signature validity, and DMARC alignment. This is where a sent email can still fail, for example when DKIM signs with one domain but the visible From domain differs.
- Validate authentication in DNS. Tools such as MXToolbox look up SPF, DKIM, and DMARC records directly in DNS and alert on common breakages. Postmark DMARC Digests turns DMARC aggregate XML reports into readable summaries.
- Monitor blocklists and reputation indicators. Spamhaus checks help you spot listings that cause sudden delivery drops. Google Postmaster Tools and Microsoft SNDS add mailbox-provider visibility for the Gmail and Outlook.com ecosystems.
- Trend changes and correlate to sending behavior. The best setups run continuous monitoring, then correlate dips to volume spikes, new sending sources, list quality issues, or content changes. If your outbound stack includes verification and deliverability-focused sending, these tools confirm whether improvements actually move placement.
Quick comparison: 10 email deliverability tools
The numbers organize ten different use cases; they are not a performance ranking. Start with the category that matches the question you need to answer.
| Tool | Category | Standout feature | Free tier | Starting price |
|---|---|---|---|---|
 GlockApps |
Placement testing | Seed-based inbox vs spam placement tests with spam filter diagnostics | Yes | $59/mo equivalent, billed annually ($708/year) ✓ |
 Mailtrap |
DNS/transactional diagnostics | Sandbox testing plus production email logs and deliverability checks | Yes | $14/mo billed annually (Sandbox); $15/mo (Email API) ✓ |
 Mailgun Optimize |
Placement testing | Placement tests, spam troubleshooting and reputation monitoring in one suite | No (first month free) | $49/mo ✓ |
 Validity Engage |
All-in-one (enterprise) | Enterprise inbox placement, reputation monitoring and sender certification path | Not published | Pricing on request |
 Folderly Inbox Insights |
Placement testing | Automated placement reports with IP, blocklist, and DNS checks | Yes (2 tests/mo) | $79/mo ✓ |
 Google Postmaster Tools |
Provider-native monitoring | Gmail spam rate, authentication, compliance, and delivery errors | Yes (fully free) | Free |
 Microsoft SNDS |
Provider-native monitoring | IP-level Outlook.com data and Junk Email Reporting Program access | Yes (fully free) | Free |
 MXToolbox |
DNS diagnostics | SPF, DKIM, DMARC lookups and blocklist checks with monitoring alerts | Yes (one monitor) | $129/mo ✓ |
 Postmark DMARC Digests |
DNS diagnostics | Parses DMARC aggregate reports into readable summaries by source | Yes (limited weekly report) | $14/domain/mo ✓ |
 Spamhaus |
Blocklist monitoring | Widely referenced threat-intel blocklists; public checker for sudden delivery drops | Yes (public checker) | Free |
Prices marked with a checkmark were confirmed on the vendor's public pricing page on August 1, 2026. "Pricing on request" means the vendor did not publish a number we could verify; confirm current terms and plan entitlements before buying.
Can one platform combine inbox placement testing and suppression management?
Yes, but the capabilities may live in different plans. Mailgun Send manages bounces, complaints, and unsubscribes through suppression lists, while Mailgun Optimize adds placement tests, validation, and monitoring in the same vendor ecosystem. Mailtrap documents suppression management and mailbox-provider statistics, with availability varying by product, stream, and plan; its Email Sandbox is a pre-send testing environment rather than an independent seed-placement test. Check the exact sending and deliverability plan before treating either setup as one bundled entitlement.
GlockApps vs Validity Engage: which is better?
Choose GlockApps for accessible, repeatable cross-provider seed tests. Choose Validity Engage, formerly Everest, when a larger email program needs placement and deliverability monitoring connected to broader governance and data-quality capabilities. Validity does not publish a price, so this is a use-case comparison, not a value-for-money verdict.
How Overloop fits
Best for: outbound teams that want verification, warmup, and pacing controls in one workflow
Disclosure: we are Overloop. Treat this entry as a disclosed product-fit assessment, not an independent test result.
What it does: Overloop combines email verification, built-in warmup that sends low-volume traffic through a third-party network, pacing controls, and list hygiene in the platform used to run outbound sequences. Deliverability and domain reputation still depend on provider policies, configuration, content, recipient behavior, and sending history; these controls do not guarantee inbox placement or replace provider dashboards.
Best at: keeping verification, warmup controls, sequencing, and reply tracking in one workflow. That reduces handoffs and makes changes to lists, pacing, and campaigns easier to review.
Falls short: Overloop is not a seed-test or DMARC-report tool. It will not show you Inbox vs Spam placement by provider or parse DMARC aggregate reports. If you only need a one-off placement check or you send outside cold outbound (transactional, lifecycle), pair it with the measurement tools below rather than expecting it to replace them.
Pricing: Starter plan from $69/user/mo, Growth from $99/user/mo, Enterprise custom (official pricing, checked August 1, 2026).
Use it if: you want to consolidate outbound controls and are prepared to pair them with independent placement and provider-reputation tools.
1 GlockApps
Best for: inbox placement testing across providers
What it does: GlockApps gives you a seed list of test addresses across major mailbox providers. You send your campaign email to that list, then it reports placement (Inbox, Spam, Tabs) and flags likely causes when placement drops, such as missing authentication, a risky link, or content patterns that trigger filters.
Best at: inbox vs spam placement reports across multiple providers at once, so you can see whether a problem is Gmail-only or widespread, plus spam filter diagnostics that point to common failure modes like broken SPF/DKIM, suspicious domains, or formatting issues, and ongoing monitoring for early warning after a list import or template change.
Falls short: it will not fix reputation by itself, and it does not replace provider-native dashboards like Google Postmaster Tools or Microsoft SNDS. Use it to measure placement and identify likely triggers, then correct the root cause in your sending setup.
Pricing: Free tier; annual billing lists Essential at a $59/mo equivalent ($708/year), Growth at $99/mo ($1,188/year), and Enterprise at $129/mo ($1,548/year). Monthly billing is also available at different rates (official pricing, checked August 1, 2026).
Use it if: you run frequent campaigns and need a repeatable, cross-provider placement number before and after changes, not just a one-time snapshot.
2 Mailtrap Email Delivery Platform
Best for: transactional email testing in staging and production
What it does: Mailtrap helps you catch problems before a real customer, lead, or applicant ever sees a message. It routes app emails to a safe sandbox inbox for staging so developers and QA can inspect HTML, text, attachments, and dynamic fields without sending to real recipients, then gives you message-level logs and deliverability checks once you move to production.
Best at: transactional email quality: password resets, magic links, invoices, trial onboarding, and system alerts. A broken link, missing variable, or wrong From address creates support tickets fast, even when deliverability itself is fine, and Mailtrap catches that class of bug before launch. It also flags common authentication misconfigurations early, when fixes are cheap, and helps trace why a transactional email bounced from production logs.
Falls short: it is not a cross-provider inbox placement tester. If your problem is cold outbound reply rates rather than transactional email quality, you will get more value from a seed-based placement tool and a sending stack with built-in verification and throttling.
Pricing: Email Sandbox (testing) free tier, then from $14/mo billed annually; Email API (transactional sending) free tier, then from $15/mo (official pricing, checked August 1, 2026).
Use it if: you are a product or engineering team that owns transactional email and needs to catch bugs in staging before they become support tickets.
3 Mailgun Optimize
Best for: higher-volume senders who want a deliverability suite
What it does: Mailgun Optimize (formerly InboxReady, now part of Mailgun by Sinch) is a deliverability suite built around placement testing, spam diagnostics, and reputation signals you can track over time as volume grows, at which point deliverability stops being a one-off test and turns into a monitoring problem.
Best at: inbox placement testing with seed-based tests across major providers to see Inbox vs Spam before you scale, spam troubleshooting that diagnoses why a message filters using content and header-level signals, and reputation monitoring that catches slow domain and IP declines before reply rates drop. It fits best when you already send through Mailgun and want deliverability visibility without stitching together five separate tools.
Falls short: it is a separate paid deliverability subscription. Lower tiers cap validations and placement tests, while monitoring features vary by plan. It works with Mailgun Send or another ESP, but it does not include warmup or outbound-specific list hygiene.
Pricing: Pilot from $49/mo (2,500 validations, 25 placement tests), Starter from $99/mo, Contract custom for enterprise (official pricing, checked August 1, 2026).
Use it if: you need validation, placement testing, and monitoring in one deliverability subscription that can work with Mailgun Send or another ESP.
4 Validity Engage (formerly Everest)
Best for: enterprise deliverability and reputation governance
What it does: Validity moved Everest's inbox-placement and deliverability-monitoring capabilities into Validity Engage in July 2026. The platform is aimed at larger email programs that need deliverability monitoring connected to testing, data quality, and shared governance.
Best at: inbox placement and diagnostics at scale with drill-down into authentication alignment and provider-specific filtering, reputation and blocklist monitoring with alerts so teams respond before revenue-impacting drops, and shared reporting for programs with multiple ESPs (Salesforce Marketing Cloud, Adobe Campaign, Oracle Responsys), shared domains, regional subdomains, and separate transactional and marketing traffic.
Falls short: its documented feature set is built around governance across multiple sending streams rather than a single outbound team running one domain. Because pricing is quote-based, smaller teams need a proposal to assess whether that scope and cost fit their program.
Pricing: not published; quote-based enterprise pricing. We could not verify a public number on validity.com, so treat any figure you see elsewhere as unconfirmed until you get a quote.
Use it if: you already send at high volume across multiple ESPs or brands and need governance and auditability, not just a placement number.
5 Folderly Inbox Insights
Best for: placement tests built around outbound mailboxes
What it does: Folderly Inbox Insights runs automated placement tests across Gmail, Outlook, and Yahoo, then reports placement alongside sending-IP, blocklist, and DNS findings.
Best at: connecting a mailbox, running a repeatable test, and receiving a shareable report with provider-level placement and technical checks. The product also includes setup guidance for DNS and blocklist issues.
Falls short: the results still come from Folderly's test accounts, not your full recipient list, so use trends and before-and-after comparisons directionally. Folderly's separate mailbox-maintenance product is priced per mailbox and should not be confused with the Inbox Insights testing plan.
Pricing: Free for 2 tests per month; Inbox Insights costs $79/mo for 100 tests or $799/year (official pricing, checked August 1, 2026).
Use it if: you want an outbound-focused placement test with IP, blocklist, and DNS context in the same report. See the official Inbox Insights details.
6 Google Postmaster Tools
Best for: free Gmail deliverability diagnostics
What it does: Google Postmaster Tools provides Gmail-specific reporting for verified sending domains. Its current dashboards include spam rate, authentication, encryption, delivery errors, and compliance data; dashboard availability can change during Google's transition to Postmaster Tools v2.
Best at: showing how Gmail reports spam complaints and whether SPF, DKIM, and DMARC pass for observed traffic. Delivery Errors can surface rate limits or policy issues, while the compliance view helps bulk senders check Gmail's sender requirements. Add and verify the domain at Google Postmaster Tools.
Falls short: it covers Gmail only and does not run an inbox-placement seed test. Low volume, privacy thresholds, reporting delays, or other eligibility limits can produce missing data, so a blank dashboard does not prove either good or bad placement. Google also notes that third-party spam-rate figures can differ from Postmaster Tools.
Pricing: Free, no paid tier.
Use it if: you send any meaningful volume to Gmail addresses. There is no reason not to have this running in parallel with everything else on this list.
7 Microsoft SNDS
Best for: free Outlook and Hotmail deliverability diagnostics
What it does: Microsoft SNDS (Smart Network Data Services) gives authorized senders IP-level data for Outlook.com and includes access to the Junk Email Reporting Program. Microsoft moved SNDS to a new portal in 2026.
Best at: checking whether traffic or reputation indicators changed for IPs you control and receiving reports when Outlook.com users mark messages as junk. It is IP-centric, so confirm the exact outbound IPs first, then correlate changes with new sources, volume shifts, or list imports. Microsoft removed trap-hit counts from the data report in July 2026, so older guides that depend on that field are stale.
Falls short: it covers Outlook.com consumer mail, not Exchange Online or Microsoft 365 business tenants, and it does not explain content-level spam reasons. Pair it with seed tests and SPF/DKIM/DMARC checks for the rest of the picture.
Pricing: Free, no paid tier.
Use it if: you control the sending IPs and need Microsoft-provided Outlook.com reputation and feedback-loop data.
8 MXToolbox
Best for: fast DNS authentication and blocklist troubleshooting
What it does: MXToolbox is a diagnostics and monitoring toolkit that runs DNS lookups and reputation checks. Paste in a domain, hostname, or IP, and it returns the records and signals deliverability teams care about: SPF, DKIM, DMARC, MX, and blocklist status. It is a useful first check when provider dashboards look normal but inboxing still drops.
Best at: SPF checks that validate your record exists, parses cleanly, and references the right sending services (catching mistakes like multiple SPF records or excessive DNS lookups); DKIM lookups that confirm a selector resolves and returns a valid public key, the first thing to check after rotating keys or changing ESPs; DMARC validation that verifies the policy record is syntactically correct and published at the right host; and quick blacklist checks against many lists at once. See how these three records fit together if you are setting them up for the first time.
Falls short: the free plan is limited to one monitor and the top 30 blocklists. Teams that need more monitors, broader blacklist coverage, or delivery-analysis features need a paid Delivery Center plan. Pair it with Spamhaus for deeper blocklist investigation when a listing appears.
Pricing: Free plan; Delivery Center from $129/mo and Delivery Center Plus from $399/mo (official plan matrix, checked August 1, 2026).
Use it if: you need a fast, no-signup way to confirm SPF, DKIM, DMARC, and blocklist status right now, before reaching for a heavier suite.
9 Postmark DMARC Digests
Best for: readable DMARC reporting and source visibility
What it does: Postmark converts DMARC aggregate XML reports into readable summaries. Its free monitoring service sends a limited weekly email; the paid DMARC Digests product adds a dashboard, longer history, all mail sources and IPs, user access, and recommendations.
Best at: catching spoofing and unauthorized senders (if a random server starts sending mail claiming to be from your domain, the report surfaces it grouped by source IP and seen-from domain), misalignment that breaks deliverability even when SPF=pass appears in headers, and sending-source drift as teams add tools like HubSpot, Salesforce, Intercom, or Zendesk that send on their behalf. Start at Postmark DMARC Digests.
Falls short: it only reads reports, it does not fix DNS records for you, and it depends on your DMARC record already pointing aggregate reports to Postmark. The free version is limited to the top 10 mail sources, five IPs per source, seven days of history, and weekly email reports. If you have not set up SPF, DKIM, and DMARC yet, start with the setup guide first.
Pricing: Free weekly monitoring; DMARC Digests costs $14/mo per domain after a 14-day trial (official product page, checked August 1, 2026).
Use it if: you want to inventory every sender touching your domain and catch alignment problems before mailbox providers start filtering you.
10 Spamhaus
Best for: investigating sudden delivery drops and blocklist hits
What it does: Spamhaus is a set of widely referenced threat-intel and blocklist services. In deliverability work, you check whether a sending IP or domain appears on a Spamhaus list, and which one, then follow the listing details to the cause and the fastest fix. Start with the public checker: Spamhaus Check.
Best at: telling you when the internet has started distrusting your sending, which DMARC reports and provider dashboards will not show directly. Use it when deliverability drops suddenly, bounces mention policy or reputation, or you suspect a compromised inbox, list, or sending IP. A listing is a symptom, not a root cause: identify the exact asset listed (sending IP vs visible From domain), read the list type and evidence on the detail page, stop the behavior that triggered it, then fix authentication and source control before requesting delisting. Delisting without a real change often results in a fast relist.
Falls short: it only tells you that trust broke, not why your list quality or bounce rate got worse in the first place. Pair it a sender reputation check and DMARC reporting to find the actual cause.
Pricing: Free public checker; enterprise threat-intel data feeds are sold separately and not the focus for most outbound teams.
Use it if: deliverability drops suddenly and you need to rule out (or confirm) a blocklist hit in minutes.
Warmup tools are a separate category
Warmup changes sending activity; the tools ranked above measure placement, authentication, reputation, or blocklist signals. A warmup dashboard still does not prove inbox placement. See the separate email warmup guide for that category, its documented limits, and the controls to review before enabling it.
Also worth knowing
Two names that come up often in deliverability conversations but did not make the main list:
- Validity Sender Score: a free reputation lookup from Validity that scores a sending IP from 0 to 100, a quick sanity check before deeper diagnosis.
- Warmy.io: a standalone warmup service for teams whose sending stack has no built-in warmup layer.
Bottom line: which email deliverability tool should you pick?
There is no single best email deliverability tool. There is the right tool for the job in front of you, and most teams need two or three working together.
If you send outbound, start with controllable inputs. Overloop combines verification, warmup, pacing, and list hygiene in the sending workflow, but cannot confirm inbox placement. Add provider-native signals from Google Postmaster Tools for Gmail, Microsoft SNDS for Outlook.com, and Yahoo Sender Hub Insights for eligible Yahoo and AOL traffic, plus Postmark's free weekly DMARC monitor for sender visibility and the public Spamhaus checker for incidents.
Layer in paid testing when you need it. GlockApps, Mailgun Optimize, and Folderly Inbox Insights provide repeatable seed-placement tests for different team profiles. MXToolbox is the fast SPF, DKIM, DMARC, and blocklist check. Mailtrap covers transactional email quality in staging and production. Validity Engage is for larger programs that need governance across many sending streams.
The short version: manage controllable inputs with Overloop, measure provider signals with the free dashboards, and reach for a paid suite only when the additional diagnostics justify it. If a tool flags a real problem, pair the diagnosis with the full checklist for fixing email deliverability. Try Overloop free →