How to Measure Email Warmup with Inbox Placement Checks

A warmup program gives your team a way to introduce a sender gradually and watch what happens along the way. In MailSlurp, you can review sending activity and available inbox placement checks before deciding whether to increase the pace.

To tell whether warmup is working, compare completed checks for the same provider, read the inbox and spam counts, and investigate repeated sending failures. A rising send count alone doesn't tell you where messages landed. Here's how to read the results without turning every review into a spreadsheet project.

Start with the question each result answers

An increasing send count is easy to spot. Understanding what happened afterward takes a little more care.

• Accepted send: the configured sending provider accepted the outbound request.
• Controlled-inbox receipt: the message reached a monitored MailSlurp destination.
• Provider placement checkpoint: the sampled provider mailbox reported a placement outcome.
• Sender readiness: MailSlurp's current assessment and pacing guidance from available signals.

An accepted send doesn't turn into an inbox result simply because enough time has passed. A message can be accepted and later appear in spam, or remain unobserved during a check. Those outcomes remain useful evidence even though the accepted-send counter has already increased.

Daily controlled-inbox observations and premium provider placement also have different coverage. On eligible plans, warmup checkpoints sample Gmail, Google Workspace, Outlook.com and Microsoft 365. The warmup documentation describes the available coverage. A result from one destination isn't a stand-in for another.

Read the checkpoint before reading the percentage

Open your program under Email warmup, then find Inbox placement. A checkpoint is a placement check at a particular stage of the program. Results are labeled Baseline, Final or a checkpoint day.

Start with three details:

1. The checkpoint: compare the latest result with an earlier check for the same sender.
2. The coverage: check whether the result is complete or partial and how many checks were sent.
3. The provider counts: read inbox, spam and not received for Gmail, Google Workspace, Outlook.com and Microsoft 365 separately where your program includes them.

A check in progress isn't a completed zero-percent result. The chart includes completed and partial checks, so a point on the line can still have incomplete coverage. If the view says Placement check unavailable or No placement results yet, leave placement undecided and check the program's coverage and activity.

Not received means the check has no matching receipt for that destination. It doesn't mean spam. Look at sending failures and provider responses to distinguish a rejected send from a delayed or missing observation.

Compare the same provider across checkpoints

Compare Gmail with Gmail and Outlook.com with Outlook.com. Keep the sending connection and coverage consistent, and account for any changes to the sender or schedule between checks.

Look at what moved underneath the percentage. An extra inbox receipt with the same spam count means more mail was observed in the inbox; it doesn't show that the spam problem has gone away. With a small sample, one message can move the percentage noticeably.

MailSlurp's Sender readiness view includes baseline and latest provider percentages, with the latest sample size when available. Use those details to see whether the change repeats across checks. A sampled result helps you investigate a sender; it doesn't predict the folder chosen for every subscriber.

Turn the review into a next step

The Sender readiness section brings the suggested daily volume, goal, accepted sends and next target together. Adaptive pacing shows whether the program will increase, hold or reduce the pace. Review any attention message alongside the actual placement results before changing the schedule.

The useful question is whether the observations support the next increase. Here's how a few common patterns translate into an investigation:

• The provider repeatedly rejects sends: investigate the connection or provider restriction before changing volume.
• Sends are accepted but placement is pending: wait for the checkpoint result before judging placement.
• One provider worsens across completed checks: review that provider separately, including authentication and recent changes.
• A partial check differs sharply from a complete one: compare coverage and counts before calling it a trend.
• Checks are stable and pacing recommends an increase: review the proposed target alongside normal production traffic.

If a newly started program has no activity, check its time zone, local sending window and next scheduled send first. It may simply be waiting for the next eligible time. The warmup monitoring documentation explains these states and the available controls.

For a sender already experiencing delivery problems, the sender reputation recovery guide gives a broader diagnosis process. Pausing a warmup during an investigation can keep a connection or configuration problem from producing more failed attempts.

Why can Gmail monitoring look healthy while a check shows spam?

Google Postmaster Tools reports on mail sent to personal Gmail accounts. Its spam rate measures recipient reports, which is different from the folder observed by a placement test. Google also says data can be delayed or missing at low sending volumes. Its dashboard documentation explains why a low reported spam rate can coexist with automatic spam filtering.

Read the two results together. An empty reputation report leaves a question unanswered; it isn't a reason to dismiss a completed spam result or increase volume.

Test the campaign separately before sending it

Your finished campaign may include links, tracking and images that weren't present during warmup. MailSlurp warmup uses managed messages or a custom plain-text subject and body; custom warmup rejects links, tracking, media, scripts and template markers.

A separate inbox placement test checks that actual message through the intended sending route. MailSlurp can reuse the verified sending connection for automated placement, while manual seed list testing provides the current test addresses and marker for a send from your email platform. The inbox placement testing guide covers those steps and explains why Promotions differs from spam.

For HubSpot, first confirm whether you warmed a connected mailbox or the route carrying marketing email. The HubSpot warmup guide explains the distinction. If the campaign comes from Mailchimp, follow the Mailchimp placement walkthrough to send the finished message to the current test audience.

Before launch, review the campaign's phone and desktop previews and check its links and images with Email Audit too. Placement tells you where the email arrived; these checks help you catch what a reader will see when they open it.

For an existing program, start with its latest completed checkpoint and the individual provider counts. If you're choosing a service, explore MailSlurp email warmup for the setup and plan options. Warmup is available on Pro and Growth, with usage beyond included sending credits billed separately.