Inbox Placement Testing

An email can be “delivered” and still end up in the spam folder, where nobody reads it. Inbox placement testing shows you where your mail really lands at Gmail, Outlook, Yahoo and others. This playbook shows you how to run a test, read the results, and fix what they reveal.

Delivered is not the same as inbox

• Delivery rate is the share of emails the receiving server accepted instead of bouncing (sending back as undeliverable). An email in the spam folder still counts as delivered.
• Inbox placement rate is the share of emails that reached the inbox, where people see them.

So a high delivery rate can hide a big problem. Only a placement test shows the difference.

Before you test: check your setup

First send one email to the Mailwel test inbox. It shows whether your authentication passes:

• SPF (a DNS record listing the servers allowed to send for your domain)
• DKIM (a digital signature proving the email came from your domain, unchanged)
• DMARC (a DNS record telling receivers what to do when those checks fail)

Fix any failures before you test placement.

How seed testing works

A seed list is a set of test mailboxes at different providers that you control. You add these addresses to a real campaign. After the send, you check each mailbox and note where your email landed.

Build a seed list

You have two options.

• Your own seed accounts. Create two or three test mailboxes at each provider your subscribers use: Gmail and Google Workspace, Outlook.com and Microsoft 365, Yahoo and AOL, Apple iCloud, and large local providers. Log in now and then, read some mail, and mark some as “not spam”. Providers treat unused mailboxes differently from real ones.
• A paid seed service. Services such as Validity Everest and GlockApps keep large seed lists across many providers and show the results in one report.

Run a seed test

1. Add the seeds to a real campaign, not a separate test, so they get the same treatment as your subscribers.
2. Wait for delivery. Give it 30 to 60 minutes. Some providers queue mail before they deliver it.
3. Check every seed. Log in to each mailbox, or open your service’s report. Record where the email landed: inbox, spam (or junk), a tab such as Gmail Promotions or Outlook Other, or missing.
4. Look for patterns. Is the problem at every provider or just one? Is it spam, or only a tab? Did it change since your last test?

What seed tests can’t tell you

• Personal filtering. Gmail and Outlook filter differently for each person, based on how they treat your mail. A loyal subscriber may get better placement than a seed that never opens anything.
• Timing. A Monday-morning send can land differently from a Saturday-evening one.
• Small samples. A few seeds per provider can mislead you. Trust patterns that repeat across tests.

Reading the results

What each result means

• Inbox (Gmail Primary, Outlook Focused): the best result.
• A tab (Gmail Promotions, Outlook Other): normal for marketing email, and not spam. Many people browse these tabs. Gmail’s promotion annotations (special markup in your email) change how you look inside the Promotions tab. They don’t move you to Primary.
• Spam or junk: a real problem. Use the table below to find the cause.
• Missing: the provider dropped or delayed the mail.

Common patterns and their causes

Pattern	Likely cause	Where to look
Spam at every provider	A blocklist listing, or broken authentication	Blocklists, then SPF, DKIM and DMARC
Spam at Gmail only	Gmail doesn’t trust your domain yet, or your spam rate is high	Google Postmaster Tools
Junk at Microsoft only	Your sending IP has a poor reputation at Microsoft	Microsoft SNDS
Spam on some sends, not others	Other senders on your shared IP are hurting it	Ask your email provider
Missing at one provider	The provider is slowing you down or dropping mail	Bounce logs, especially codes starting with 4

A blocklist is a public list of IPs and domains that send spam. A shared IP is a sending address your email provider uses for many customers, so their behaviour affects you.

Tools to monitor between tests

Seed tests are snapshots. These tools show daily trends.

• Google Postmaster Tools shows how Gmail sees your mail: your spam rate, authentication and delivery errors. Keep the spam rate below 0.1%. See the Google Postmaster Tools guide.
• Microsoft SNDS (Smart Network Data Services) rates your sending IPs green, yellow or red for Outlook.com. It also reports spam trap hits (mail to addresses that never signed up for anything).
• Blocklist checkers such as MXToolbox and Multirbl check many blocklists at once. Spamhaus, Barracuda and SpamCop matter most.
• Mailwel’s tools: the test inbox for authentication, DNS lookup for your records, the SMTP probe to see how a provider’s server responds, and the header analyzer to trace a message.

How often to test

Check	How often	Why
Seed placement test	Every major campaign	See placement trends
Google Postmaster Tools	Daily	Spot a rising spam rate early
Microsoft SNDS	Daily	Spot IP problems at Outlook.com
Blocklist check	Several times a day, automated	Catch a new listing quickly
SPF, DKIM, DMARC check	Weekly	Catch broken records
Full review	Every three months	Look at everything together

Set alerts for a new blocklist listing, a Gmail spam rate above 0.1%, and a jump in bounces.

Fixing what you find

• Authentication. Repair your records and switch on DKIM signing. Make sure the signing domain matches your From address (this is called alignment).
• Reputation. Send less for a while, and only to people who opened or clicked recently. Remove addresses that never engage. Find out which emails draw complaints.
• Content. Send a plain version to see whether content matters. Check the reputation of every linked domain. Remove suspect parts one at a time.
• Infrastructure. Ask your email provider whether your shared IP’s reputation dropped. At high volume, consider a dedicated IP (one only you use), warmed up slowly.

Checklist

• Send a test to the Mailwel test inbox and fix any SPF, DKIM or DMARC failure.
• Set up seed mailboxes at Gmail, Microsoft, Yahoo and Apple, or sign up for a seed service.
• Add seeds to your next real campaign and record where each copy lands.
• Treat tabs as normal. Treat spam and missing as problems.
• Verify your domain in Google Postmaster Tools and register your IPs in Microsoft SNDS.
• Automate blocklist checks and alerts.
• Repeat the seed test with every major campaign and compare results over time.