Inbox placement testing

Inbox placement testing measures where a real campaign email lands after it is sent. MailSlurp supplies controlled seed addresses at major personal and business inbox providers, matches the message using a unique test code, and reports whether each copy reached primary, promotions, spam, or was not received.

Use this workflow before an important launch, after changing a sending domain or provider, when a campaign unexpectedly reaches spam, or when you need provider-level evidence alongside content and domain checks.

Provider guides

Provider guides show how to place the current test marker and seed recipients into a campaign platform, send the published email, and interpret the result. This table will expand as more provider workflows are added.

Provider guide	Workflow
Braze	Add the current seeds to a Braze Seed Group, send the marked campaign, and compare provider placement
Brevo	Add the current seeds to the Brevo Test List, send the marked email, and compare provider placement
Constant Contact	Import the current seeds into a dedicated list, send the marked campaign, and review provider placement
GetResponse	Import the current seeds into a dedicated list, send the marked newsletter, and review provider placement
HubSpot	Import the current seeds as marketing contacts, send the marked email, and review provider placement
Kit	Import the current seeds under a dedicated tag, send the marked Broadcast, and review provider placement
Klaviyo	Import the current seeds into a consented list, send the marked campaign, and compare provider placement
Mailchimp	Tag the current seeds in an audience, send only to that segment, and review provider placement
MailerLite	Import the current seeds into a dedicated group, send the marked campaign, and review provider placement
Mailjet	Import the current seeds into a dedicated contact list, send the marked campaign, and review provider placement
Omnisend	Import the current seeds into a segment, send the marked campaign, and review provider placement
Salesforce	Add the current seed addresses to an opted-in Actionable List, publish the marked email, and review provider placement

Run an inbox placement test

1. Open Inbox placement in the MailSlurp dashboard.
2. Create a new test and copy its unique marker.
3. Copy every seed address supplied for the run.
4. Put the exact marker in the campaign subject or body.
5. Send the same campaign to all current seed addresses.
6. Keep the result page open while MailSlurp resolves provider outcomes.
7. Review the delivery score, placement rows, content issues, and domain issues.

Each run has its own marker and seed set. Use the values displayed by the active test rather than reusing details from an earlier run.

Understand placement results

Result	Meaning
Primary or inbox	The message reached the provider’s main inbox experience for that seed
Promotions	The provider delivered the message to a promotional category
Spam or junk	The provider classified the message as unwanted or suspicious
Not received	MailSlurp did not observe the message at that seed during the test window
Pending	The provider result is still being checked

Promotions is a delivered result, but it is different from primary-inbox placement. Interpret it in the context of the campaign: a product announcement may reasonably appear in promotions, while an expected account or security message may need a different outcome.

Review content and domain signals

Open Content issues for message-level findings and Domain issues for sender and domain checks associated with the run. Use these findings to choose a specific next change, such as correcting authentication, replacing a broken link, improving sender consistency, or adjusting the campaign content.

Inbox placement is affected by sender reputation, SPF, DKIM, DMARC, list quality, engagement, volume, message content, and provider-specific filtering. Retest the exact revised campaign after a meaningful change.

Inbox placement and deliverability tests

Inbox placement and expectation-based deliverability tests answer different questions:

• Inbox placement sends a campaign to controlled provider seeds and reports folder outcomes.
• Deliverability tests use MailSlurp inboxes and expectations to verify that a message arrives and contains the required subject, recipients, headers, links, attachments, or body content.

Use inbox placement for provider-folder evidence. Use deliverability tests for repeatable application and message assertions. Teams often use both alongside device previews so the same release is checked for arrival, placement, and visual rendering.

If a result stays pending

Wait for the observation window to complete. Confirm that the exact marker was present in the delivered email and that every current seed address was included in the send. A delayed or not-received result is useful evidence and should not be replaced with an assumed placement.

Before the next campaign

• send only to permissioned and engaged recipients
• authenticate the sending domain with SPF, DKIM, and DMARC
• keep sender identity and reply handling consistent
• avoid sudden, unexplained volume changes
• check links, images, footer, and unsubscribe controls
• publish the final campaign revision before testing
• create a new test and use its current marker and seed addresses
• compare provider results after each meaningful correction