Definition
An email inbox placement test is a diagnostic that measures where a sender's messages actually land. The test sends a representative email to a network of controlled "seed" inboxes at major mailbox providers, then reports what proportion arrived in the inbox, the spam folder, or not at all. The result is expressed as an inbox placement rate, the most direct measure of whether email is reaching recipients.
How It Works
Inbox placement tests rely on a pool of real mailboxes that a testing provider maintains across Gmail, Microsoft, Yahoo, and other large providers. The process is straightforward:
- The sender connects the testing service to its sending platform or sends through the service's infrastructure.
- The service delivers the test message to seed inboxes across the provider network.
- The service inspects each seed inbox to determine the folder where the message landed.
- Results are aggregated into a placement report, often broken down by provider.
Because placement can vary by sender identity, the test is most accurate when it replicates the actual production send as closely as possible, including the same sending domain, email authentication setup, and message content.
Why It Matters
Inbox placement tests reveal the gap between what a platform reports as "delivered" and what actually reached the inbox. A message that is accepted by a receiving server but routed to spam still counts as delivered in many platforms, hiding a serious problem. Seed testing is therefore the ground truth for deliverability.
Placement tests are especially valuable in these situations:
- Before launching a new domain or IP, to establish a baseline.
- During email warmup, to confirm placement is improving.
- After a reputation incident, to verify recovery.
- When changing email service providers or authentication records.
Regular seed testing, typically weekly for active senders, turns inbox placement into a tracked metric rather than an assumption.
Example
A B2B software firm is about to migrate to a new ESP. Before the switch, the team runs an inbox placement test from the new platform and discovers placement at Microsoft is only 62 percent, caused by a missing DKIM signature. After correcting the record, a retest shows 97 percent placement, and the migration proceeds safely.
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Frequently Asked Questions
They are the same thing. "Seed testing" is the informal name for sending to controlled test mailboxes; "inbox placement test" is the more formal term for the measurement it produces.
They are a strong approximation but not a perfect mirror of real-world delivery, because actual subscriber engagement and mailbox history also influence placement. Treat results as a reliable directional signal rather than an exact guarantee.
Commercial services typically maintain thousands of seed inboxes across many providers and regions. More coverage produces more granular results, such as placement broken out by specific mailbox provider.
Healthy senders typically achieve 95 percent or higher. A rate below 90 percent signals a meaningful problem with reputation, list quality, or authentication that warrants immediate attention.