How to Test Your Email Deliverability (Inbox or Spam)
What an inbox placement test is, how seed mailboxes work and how to check whether your emails reach the Inbox or Spam.
What Email Deliverability and Inbox Placement Mean
When you send an email, your server may report it as "sent successfully" — but that does not mean it reached the recipient's inbox. It may have landed in Spam, in a tab (Promotions) or been silently rejected. The gap between "sent" and "delivered to the inbox" is called inbox placement — and it's what actually matters.
An inbox placement test (or "seed test") shows you, across real accounts at different providers (Gmail, Outlook, Zoho, etc.), which folder your message ended up in.
How a Seed Test Works
The logic is simple and objective:
- You start a test and get a unique subject (ID) and one or more seed mailboxes.
- You send a normal email from your system to those addresses, using the exact subject.
- The tool connects to the seed mailboxes (over IMAP, or the provider's API — e.g. Microsoft Graph for Outlook), finds the message by its unique subject and checks which folder it landed in — Inbox or Spam.
- It computes an inbox placement score and reads the headers for the SPF/DKIM/DMARC verdict as the recipient saw it.
See live where your emails land — Inbox or Spam:
→ Email Deliverability TestStep by Step with NerdTools
- Open the Email Deliverability Test and hit "Start test".
- Copy the subject and the addresses it gives you.
- Send an email from the real system you want to test (mail server, newsletter, app). Write a normal, everyday message in the body — not empty or "test", which skews the result.
- Keep the page open; the result appears automatically when it arrives. The link stays live for 14 days, so you can save or share it.
How to Read the Result
- Folder per provider: Inbox (✓), Spam (⚠) or "not arrived".
- Inbox Placement Score: the percentage of seeds where you hit the inbox.
- SPF / DKIM / DMARC: the authentication verdict as the recipient saw it.
- SpamAssassin score (where available): an objective "how spammy" signal for your content, with the rules that fired.
Important: At the large providers inbox placement is personalised per engagement (how much each recipient opens/replies to your mail). A result from fresh seed mailboxes is indicative — it shows whether you pass the technical filters, not an absolute guarantee for every recipient.
What to Do if You Land in Spam
The test shows you the "where"; for the "why", start with the basics:
| # | Check | Tool |
|---|---|---|
| 1 | SPF/DKIM/DMARC correctly set up | SPF/DKIM/DMARC |
| 2 | IP/domain not on blacklists | Blacklist Checker |
| 3 | Headers of a real email | Mail Headers |
| 4 | Reverse DNS (PTR) of the mail server | DNS Lookup |
In depth: Why Are My Emails Going to Spam?
Tips for Stable Inbox Placement
- Authentication: SPF with
-all, 2048-bit DKIM, DMARC at leastp=quarantine. - Reputation & warm-up: new domain/IP? Ramp volume up gradually — providers distrust senders with no history.
- Content: avoid spam-trigger words, excessive links/images and broken HTML; include an unsubscribe link for bulk mail.
- List hygiene: remove bounces and inactive recipients — spam reports wreck your sending reputation.
Frequently Asked Questions
How do I know if my emails go to Inbox or Spam?
Run an inbox placement test: send an email to seed mailboxes with a unique subject and see which folder it was delivered to. The Email Deliverability Test does this automatically and gives a score + SPF/DKIM/DMARC.
Why is the score called "indicative"?
Large providers decide inbox placement partly from each recipient's engagement history. Fresh seeds mainly show whether you pass the technical filters — not an absolute guarantee.
What should I write in the test email body?
A normal, everyday message like you'd really send. Empty or "test"-looking content can land in spam by itself and skew the result.
Is there a free mail-tester or GlockApps alternative?
Yes — NerdTools' Email Deliverability Test runs a seed-based inbox placement test with a score, SpamAssassin and SPF/DKIM/DMARC verdict, for free.