A real email deliverability test sends your message to a set of seed addresses across Gmail, Outlook, Yahoo, and business domains, then reports where each one landed: primary inbox, Promotions, spam, or blocked. A spam score out of 10 is not that.
A real email deliverability test sends your message to a set of seed addresses across Gmail, Outlook, Yahoo, and business domains, then reports where each one landed: primary inbox, Promotions, spam, or blocked. A spam score out of 10 is not that. Mail-tester scores your content against SpamAssassin only, which is useful for catching obvious problems but tells you nothing about actual placement.
If you only check a spam score, you can pass at 9 out of 10 and still be in spam at every major provider. This post covers how to run a placement test, which tools do what, what a healthy result looks like, and why a test can pass while your real campaign still gets foldered.
An email deliverability test measures where a message actually lands after sending: the primary inbox, a secondary tab, the spam folder, or a hard block. It uses seed inboxes across major mailbox providers and reports placement per provider, alongside authentication checks, blacklist status, and content analysis. It differs from a spam score, which only rates content against a filter ruleset.
It is a live send to a controlled set of mailboxes you can inspect. The tool gives you a message or an address list, you send your real campaign email to it from your real sending mailbox, and it reports back:
The placement report is the part that matters. Everything else is diagnostic detail for when placement is bad.
This is the distinction that trips people up. A spam score, like the one mail-tester gives free, is a content check against SpamAssassin rules. It catches spammy words, broken authentication, and missing unsubscribe headers. It does not send to real provider inboxes, so it cannot tell you that Gmail is foldering you on reputation.
An inbox placement test, like GlockApps Inbox Insight, sends to 70 to 100+ real seed addresses across providers and reports exactly where each message lands. That is the number that reflects what your prospects experience.
Use the spam score as a cheap pre-check. Use a placement test to know if you have a problem. See spam score checker and inbox placement test.
Six steps.
1. Pick a tool. Mail-tester for a free content pre-check. GlockApps, Mailgenius, or Inbox Monster for real placement.
2. Use your real campaign email. Send the actual message you plan to use, subject line and all, not a "test test test" blob. Filters weight content, and a dummy message gives a dummy result.
3. Send from your real sending mailbox. The same warmed mailbox on the same secondary domain you run campaigns from. Testing from a different account tells you about that account, not your fleet.
4. Read placement by provider. Gmail and Outlook are the two that matter most for B2B. If either shows spam or Promotions, you have a target to fix.
5. Check the diagnostics. Confirm SPF, DKIM, and DMARC all pass, run an email blacklist check, and review the content flags.
6. Repeat on a schedule. Weekly during domain warm-up, then monthly and before any major campaign.
| Tool | What it tests | Rough price |
|---|---|---|
| Mail-tester | Content vs SpamAssassin, auth, blacklist | Free, paid tiers for volume |
| GlockApps | Real seed placement (~70 to 100+ inboxes), IP chain, content | ~$59 to $129 / month |
| Mailgenius | Seed placement plus deliverability checklist | Free basic, paid for depth |
| Inbox Monster | Enterprise seed placement and monitoring | Custom |
| MailReach spam test | Placement check bundled with warm-up | Included in warm-up plans |
Mail-tester is the best free content check; the others test actual mailbox placement.
Anything below that is a specific fix, not a vague worry. Spam at Gmail with clean auth points to reputation or engagement. Promotions-tab placement points to content and link density. A blacklist hit points to infrastructure. See why are my emails going to spam and email domain reputation check.
Weekly while a domain is warming, because that is when placement moves fastest. Then monthly for steady-state monitoring. Always run a test before launching a large campaign, after any change to your sending setup, and when onboarding a new sending domain. See how to improve email deliverability.
A deliverability test is a smoke detector, not a guarantee. Three reasons it can read clean while real sends struggle.
Seed inboxes are not your recipients. They have no history with your domain, no prior opens, no replies. Your real prospects' filters weigh personalized engagement signals that seeds cannot reproduce.
Engagement is per-recipient. A seed test cannot tell you that a specific company's mail server quarantines external senders, or that a segment of your list never opens anything.
Catch-all and corporate filters vary widely. A message that lands in a personal Gmail seed can still be held by a strict enterprise gateway. See what is a catch-all email domain.
Treat a passing test as "no obvious problem," then watch your real campaign's open and reply rates as the true signal.
When placement comes back bad, fix in this order, because each step rules out a cause before you spend time on the next.
Working top to bottom keeps you from rewriting copy when the real issue was a broken DKIM record.
The Seed-Over-Score Rule: a spam score rates your content; a seed placement test tells you where your mail actually lands. Only the second one can tell you that you have a deliverability problem, so never stop at the score.
The rule matters because the free spam score is the test most people run, and it is the one most likely to give false comfort. It was designed to catch content and authentication mistakes, and it is good at that. It was never designed to detect that Gmail has quietly decided your domain is low-reputation and is foldering you regardless of how clean the message is.
When someone says "my deliverability tester says I'm fine but my replies dropped," this is almost always what happened: they checked a score, not a placement. The quotable version: "A 10 out of 10 spam score and a spam folder are not a contradiction. They measure different things."
Run the score to catch the obvious. Run a seed placement test to know the truth. Then trust your live open and reply rates over both.
A deliverability test can tell you that your domain reputation is slipping. It cannot fix the cause, which is usually a list full of dead addresses and unengaged contacts driving bounces and complaints.
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Running an email deliverability test means sending your real campaign message from your real mailbox to seed inboxes across providers and reading where it lands, not just checking a spam score. Use mail-tester as a free content pre-check, then run a seed placement test with GlockApps or a similar tool to see actual inbox versus spam placement per provider. Test weekly while warming a domain and before every big campaign. And remember the test is a smoke detector: your live open and reply rates are the real verdict.
How do I test my email deliverability?
Send your real campaign message from your real sending mailbox to a seed list across Gmail, Outlook, Yahoo, and business domains, using a tool like GlockApps or Mailgenius. Read the placement report per provider, confirm SPF, DKIM, and DMARC pass, and check blacklist status. Repeat weekly during warm-up and before major campaigns.
What is the difference between a spam score and a deliverability test?
A spam score, like mail-tester's, rates your content and authentication against a filter ruleset such as SpamAssassin. A deliverability test sends to real seed inboxes and reports where the message actually lands. You can score 10 out of 10 and still be in the spam folder, because the score cannot see your domain reputation.
Is mail-tester enough to check deliverability?
No, on its own. Mail-tester is an excellent free content and authentication check, but it scores against SpamAssassin rather than sending to real provider inboxes. Pair it with a seed placement test that reports inbox versus spam placement at Gmail and Outlook, which is where B2B deliverability is won or lost.
How often should I run a deliverability test?
Weekly while a sending domain is warming up, since placement changes fastest then. Monthly once the domain is established, and always before a large campaign, after any change to your sending configuration, and when adding a new sending domain to your fleet.
Why does my email pass the test but still go to spam?
Seed inboxes have no history with your domain and cannot reproduce the personalized engagement signals that real recipients' filters weigh. Corporate and catch-all filters also vary widely. A passing test means no obvious problem; your live campaign's open and reply rates are the real measure.
What is a good inbox placement rate?
Primary inbox placement on 90% or more of your Gmail, Outlook, and business-domain seeds, with authentication passing and no blacklist listings. Below 90%, or any pattern of spam or blocked results at a single major provider, means a specific issue to diagnose, usually reputation, content, or infrastructure.
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