Best Email Deliverability Testing Tools

Key takeaways:

• “Deliverability testing” covers four different checks: inbox placement, authentication and records, server and connection, and reputation and blocklists. Most failed diagnoses come from running the wrong one.
• Work in a fixed order: confirm the server is sending properly, verify SPF, DKIM, and DMARC for the exact From domain, check blocklists and reputation, run a placement test, and score content last.
• This list ranks tools by breadth across the four categories first, then depth within a category, then accessibility. A single-category specialist can beat a broader tool inside its own lane.
• Google Postmaster Tools is the only source of real Gmail spam-rate data, and Mail-Tester and MxToolbox are useful free first checks. Paid tools earn their place when problems recur, volume is high, or continuous monitoring is needed.
• A clean spam score or a single placement result is not a guarantee of inbox delivery. Run more than one test, use your real sending platform, and change one variable at a time.

Disclosure: This roundup was written by a contributor from PowerDMARC, an email authentication platform, which appears first in the list. The ordering criteria are set out below so readers can judge the ranking for themselves.

“Deliverability testing” covers at least four different kinds of tests, measuring four different things, and most people start with the wrong one. A spam-score checker won’t reveal a broken SPF record, and a record checker won’t tell you your last campaign landed in Promotions.

That mismatch explains a familiar waste of time. A team rewrites subject lines for a week when the actual fault is a DKIM key that stopped validating after a DNS change. Below are ten email deliverability tools worth knowing, ordered by how much of the diagnostic picture each one covers. Each entry says what the tool is good for and where it falls short.

What Deliverability Testing Actually Measures (and How This List Is Ordered)

An email deliverability test can mean any of four checks, and the tools in this article are built around one or more of them. Knowing which check answers which question saves more time than any single product choice.

Inbox Placement

An inbox placement test sends a message to a panel of seed mailboxes at different providers and records where it lands: inbox, spam, a tab such as Promotions, or nowhere at all. It tells you the outcome but not the cause.

Seed mailboxes are also a sample. They behave differently from real subscribers because mailbox providers lean heavily on engagement history, and a freshly created seed account has none. Treat a placement result as strong evidence, not a verdict.

Authentication and Records

SPF declares which servers may send for a domain. DKIM signs each message so tampering is detectable. DMARC tells receiving servers what to do when a message fails both checks or fails to align with the visible From domain.

The failures here are usually mundane. A new sending platform never got added to SPF. The SPF record has grown past the ten DNS lookups it is allowed. A DKIM selector was never published. The From domain doesn’t align with the domain that passed.

Each one can push mail to spam or get it rejected while the content is perfectly fine. Tools in this category read DNS records and message headers rather than scoring copy.

Server and Connection

This category asks whether the sending server responds correctly, supports TLS, has a matching reverse DNS (PTR) record, and presents valid MX records. A misconfigured server produces bounces, deferrals, or silence, and no amount of content scoring will see it. Google’s own Postmaster documentation lists encryption and missing PTR records among the problems it reports, which gives a sense of how routine these faults are.

Reputation and Blocklists

Reputation covers whether a domain or IP appears on blocklists and how mailbox providers rate the sender over time. The trend matters more than any snapshot. A slow rise in spam complaints shows up in reputation data weeks before it shows up in placement.

How This List Is Ordered

The ordering criteria are, in priority order:

1. Breadth of diagnosis across the four categories above.
2. Depth within a category, meaning how much the tool can tell you once it points at a problem.
3. Accessibility, which favors free tiers and no-signup tools for readers who need one quick answer.

The ranking measures breadth, not overall quality. A specialist that covers a single category can beat a broader tool inside its own lane, and several entries below do exactly that. They sit lower because they answer fewer of the questions a stalled campaign raises, not because they do the work worse.

The Practical Rule: Authentication First, Content Last

Start at authentication, because a failure there can cause every other symptom. Rule out server faults next. Treat content scoring as the last mile, useful once the foundation is confirmed sound. Most people run this order in reverse, which is why the same fixes get applied repeatedly with no change in results.

The ten tools at a glance

1. PowerDMARC

PowerDMARC leads this list because of breadth, not because it wins every category. It covers placement testing, authentication validation, and connection testing in one suite rather than a single test type, which is exactly what the first ordering criterion rewards.

The email deliverability tester sends a message to seed mailboxes across Gmail, Outlook, Yahoo, iCloud, AWS Mail and Zoho. It reports where the message landed and whether SPF, DKIM, DMARC, and BIMI passed, in one pass. Seeing both results side by side matters because the two questions are linked. A message that lands in spam with a DKIM failure needs a different fix from one that lands in spam with every check passing, and a single-purpose tool answers only half of that.

Server-level testing is the check most marketers skip when nothing is arriving at all. An SMTP test separates a fault in the sending server, such as a failed handshake, missing TLS, or a broken reverse DNS record, from a filtering problem downstream. Without it, a team can spend days rewriting copy for a message that never left the server properly.

When a message did arrive but went to spam, the raw headers usually explain why. An email header analyzer parses the authentication results the receiving server recorded, along with the path the message took, which makes an alignment failure or an unexpected relay much easier to spot.

Beyond one-off tests, the platform provides continuous DMARC aggregate report monitoring, so a new unauthorized sender surfaces as an alert rather than as a client complaint. That matters for deliverability because drift is the usual cause of a slow decline. A marketing team adds a new tool, nobody updates SPF, and pass rates erode over several weeks.

Best for: teams that want authentication and placement diagnosed together instead of assembled from separate tools.

Limitation: the platform is built around domain authentication, so content and copy-level spam scoring is not its focus. Pair it with a content scorer for that layer.

2. Google Postmaster Tools

Google Postmaster Tools is a free service that shows how Gmail sees a sending domain. According to Google’s Postmaster Tools documentation, it includes a compliance status dashboard measured against Google’s sender requirements, plus dashboards for user-reported spam rate, authentication, encryption, and delivery errors, along with domain and IP reputation ratings.

The compliance view has a useful split. Google defines a bulk sender as one sending about 5,000 or more messages to Gmail accounts in 24 hours, and some requirements, including DMARC authentication and one-click unsubscribe, apply only to those senders.

The spam rate dashboard deserves a careful read. It reflects the share of inbox-delivered messages that recipients mark as spam. Google notes that the figure can look deceptively low when Gmail is already filtering much of your mail to spam, because people see fewer of your messages to report. A low rate next to a poor reputation is therefore a warning sign, not reassurance.

No third-party tool can approximate this data, because Google is the only party that sees Gmail user behavior in aggregate. Google’s documentation says as much, noting that third-party spam reports typically differ from what the dashboard shows.

Best for: seeing your actual Gmail spam complaint rate and checking whether your setup meets Gmail’s published requirements.

Limitation: it covers Gmail only, requires domain verification, and the reporting is delayed. Google says data typically updates within 24 hours but can take longer, and dashboards can show little or nothing on low-volume days.

3. GlockApps

GlockApps is a seed-list inbox placement tester. You send a message to the addresses it provides and receive a report showing placement by provider and folder, including details such as whether a Gmail message reached the Primary tab or Promotions. It also runs content and spam filter analysis on the same test.

It suits the campaign-by-campaign question of whether a particular send will reach the inbox. Running it before a large send, from the same platform that will send the real campaign, catches problems while they are still cheap to fix.

Best for: placement questions on specific campaigns and pre-send checks.

Limitation: seed panels are not your real subscriber list, and results shift between sends. Run more than one test and read the pattern instead of any single result.

4. Mail-Tester

Mail-Tester is a free single-message spam scorer. It gives you a one-time address; you send a message to it, and it returns a score out of ten with a plain breakdown of what cost points. The checks run through SpamAssassin-style rules and cover authentication signals, blocklist lookups, and HTML structure.

Its strength is speed and clarity. With no signup and no configuration, a marketer with no idea where the problem sits can get a first read in a couple of minutes. The free tier caps the number of tests per day, which is fine for a spot check and limiting for anything systematic.

Best for: a fast first read when you have no idea where the problem is.

Limitation: it scores one message against heuristics, not real placement. A good score does not mean inbox delivery, and a mediocre one may not mean spam.

5. Validity Everest

Validity Everest is an enterprise platform that brought together what were previously separate Validity products, including 250ok and Return Path, with the company’s BriteVerify list verification. It combines inbox placement monitoring by mailbox provider, sender reputation monitoring, blocklist and spam trap alerting, list validation, and a Sender Certification program.

The value is depth across an entire email program rather than a single test. Placement data, reputation signals, and list quality sit in one place, which lets a dedicated team correlate a drop in placement with a change in list source or sending pattern.

Best for: high-volume senders with a dedicated deliverability function.

Limitation: it is priced and scoped for enterprise, and it is heavier than most teams need. A small program would spend more time configuring it than learning from it.

6. Litmus

Litmus is best known for rendering previews across email clients, showing how a message looks in different apps and devices. It also includes spam filter testing, which puts a light deliverability check alongside the design review.

That combination is practical for teams where deliverability questions are tangled up with design and QA. Heavy images, broken layouts, and clipped messages are content problems that Litmus surfaces well.

Best for: teams whose deliverability questions are entangled with rendering and design QA.

Limitation: it is strongest on rendering and is not a root-cause authentication diagnostic. If mail is failing DMARC, Litmus won’t say so in the detail needed to fix it.

7. MxToolbox

MxToolbox is a long-standing set of blocklist checks and DNS and mail server diagnostics. Its lookups cover MX records and the SPF, DKIM, and DMARC records; its blocklist check queries a long list of public blocklists at once, and it includes SMTP diagnostics for testing a mail server’s response.

When delivery suddenly collapses, a blocklist entry is the first thing to rule out, and this is the most familiar place to do it. The lookup tools are also handy for a fast sanity check on a single record.

Best for: sudden delivery collapse, where a blocklist listing is the first thing to eliminate.

Limitation: the interface is dated, and the free tier is limited. Not all listed blocklists carry equal weight either. A listing on a widely consulted list such as Spamhaus is a very different matter from one on a small list few receivers check, so identify which list before treating a result as urgent.

8. MailReach

MailReach combines email warm-up with deliverability monitoring. Warm-up exchanges engagement with a network of other mailboxes to build a sending history for a new mailbox, while its spam tester checks where messages land and its monitoring flags changes in placement, DNS, and blocklist status.

It’s built for the situation where a domain has no history. A newly provisioned sending domain starts with no reputation, and sending volume before that reputation exists is the classic route to the spam folder.

Best for: cold outreach and newly provisioned sending domains.

Limitation: the focus is narrow. It handles warm-up and monitoring, not a full diagnosis across authentication, server, and reputation categories.

9. Mailtrap

Mailtrap started as an email sandbox. It captures messages sent from staging and development environments so developers can inspect them without reaching real recipients, and it can check spam score, validate headers, and test HTML and CSS support across email clients. It has since grown into a sending platform as well.

Its natural use is catching mistakes before launch: a password reset with a broken link, a receipt template with missing data, a header that would trigger a filter. Through its API, it can also slot into automated tests.

Best for: developers validating transactional email before it goes live.

Limitation: it is built for pre-production testing, so it answers less about live campaign placement. It can tell you a message is well formed, not where Gmail will put it once it is out in the world.

10. Folderly

Folderly focuses on ongoing placement monitoring with remediation guidance. It runs placement tests, monitors authentication records for configuration drift, and analyzes content for spam triggers, then explains what appears to be causing a problem and what to change. Its orientation is toward outbound and cold email teams protecting sender reputation across many mailboxes.

The appeal is continuity. Where most email deliverability tools give a point-in-time reading, this one keeps checking and flags a change when it happens, which helps when a problem develops gradually.

Best for: teams wanting continuous monitoring rather than point-in-time tests.

Limitation: the core product is subscription-based with no meaningful free tier for a one-off diagnosis. If you have a single problem to solve today, it is more than you need.

How to Choose Between These Email Deliverability Tools

You don’t need a tool from every category. You need the one that matches the problem in front of you. The symptom usually tells you where to look:

• Emails not arriving at all: start with connection and authentication testing. Nothing downstream matters until the message leaves the server properly.
• Emails arriving but landing in spam or Promotions: run a placement test, then check reputation data.
• Only one recipient domain is affected: open that provider’s own postmaster data first, since each mailbox provider judges senders differently.
• Open rates fell with no change on your side: check for authentication drift or a new sending source, such as a platform someone added without telling the email team.

A Step-by-Step Order for Diagnosing a Deliverability Problem

Working in a fixed sequence prevents the common trap of changing three things at once and not knowing which one helped.

1. Confirm messages are leaving the server. Read bounce and deferral messages, and run a connection or SMTP test. If the server is failing, stop here and fix that.
2. Check authentication for the exact From domain. Verify SPF, DKIM, and DMARC, and confirm that each sending platform is covered. Then open the headers of a delivered message and read the authentication results the receiver recorded, since these show what actually happened rather than what your DNS says should happen.
3. Check blocklists and reputation. Run a blocklist lookup on both the sending domain and the sending IP, and read the postmaster data for the mailbox providers your list uses most.
4. Run an inbox placement test using the real sending path. Send from the platform that sends your campaigns, not from a personal mail client, and note any differences between providers.
5. Score the content last. Look at links, image weight, subject lines, and unsubscribe handling, using a scorer as a guide rather than a judge.
6. Retest after each change, one variable at a time. Allow time for results to move. Google notes that compliance data can take up to 7 days to reflect changes, and DNS changes need time to propagate.

What to Look for in a Tool

Match the tool to one of the four categories first. Then check a few practical points:

• Does it test through your real sending platform, or a simulated path that hides the authentication behavior you actually have?
• Does it use real seed mailboxes or estimates?
• Does it keep a history so you can see trends, or only show a snapshot?
• Does it explain the fix, or simply report a failure?
• Can it alert you when something changes, rather than waiting for you to look?

Free Versus Paid

Free tools handle one-off questions well. Google Postmaster Tools, Mail-Tester, and the basic lookups at MxToolbox will answer a good share of first-line questions at no cost. Paid tools earn their place when the problem recurs, when sending volume is high enough that a placement dip has a real cost, or when someone needs to monitor continuously instead of checking on demand.

Common Mistakes that Make Test Results Misleading

• Testing from a different path than production. A message sent from a personal mail client is authenticated differently from one sent through a marketing platform, so the result says little about your campaigns.
• Trusting a single run. One seed result is a data point. Two or three runs show whether a result is stable.
• Checking the wrong domain. Authentication is evaluated against the domain in the visible From address, and subdomains and third-party senders often carry their own gaps.
• Fixing content before authentication. It feels productive and rarely is.
• Treating a clean test as a guarantee. Real filtering also weighs engagement, complaint history, and sending patterns that a test can’t fully replicate.

Where to Start

The right email deliverability testing tool depends on which of the four questions is open. If mail isn’t arriving, test the connection. If it arrives in the wrong place, test authentication and placement together. If Gmail is the concern, read Postmaster Tools. If the problem keeps coming back, consider continuous monitoring.

A sensible first step is to run one authentication check and one placement test on the actual sending domain, using the real sending platform. Record the result before changing anything. That baseline turns every later fix into something measurable, and it usually points to the category where a specialist tool is worth adding.

Frequently Asked Questions

What’s the difference between a deliverability test and an inbox placement test?

An email deliverability test is the broader term and can cover authentication, server configuration, blocklists, and content. An inbox placement test is one specific kind that measures where a message actually lands across mailbox providers. A placement test tells you where a message went, while the other checks help explain why.

Can free tools diagnose a deliverability problem adequately?

For many first-line problems, yes. Free tools can confirm whether records are valid, whether a domain is blocklisted, how a message scores, and what Gmail reports about spam rates. They fall short on continuous monitoring, multi-provider placement history, and alerting. For a one-off problem, free tools are often enough.

How often should deliverability be tested?

Test before any large campaign or change to sending infrastructure, and after adding a new sending platform or domain. For established programs, a regular scheduled check, monthly for many teams, catches drift before it affects results. Programs with high volume or frequent changes benefit from continuous monitoring instead.

Does a good spam score mean my email will reach the inbox?

No. A spam score measures how a single message reads against a set of rules, not how a mailbox provider will treat it. Real placement also depends on sender reputation, engagement, complaint history, and authentication. A good score is a useful signal and nothing more.

Do SPF, DKIM and DMARC really affect where mail lands?

Yes. Authentication is the baseline that mailbox providers use to decide whether a message is really from the domain it claims, and failures commonly lead to spam placement or rejection. Google’s sender requirements list SPF and DKIM for all senders to Gmail and add DMARC for bulk senders, so authentication is now a requirement as well as good practice.

Why do two tests of the same email show different results?

Seed panels are a sample, and filtering decisions vary with time, volume, and recent sending activity. Small differences between runs are normal. Consistent differences between runs, or between providers, are the ones worth investigating.