--- title: "Inbox Placement Test Log: 7 Months of Prewarmed Data" description: "We seed-test every new batch of prewarmed inboxes before it ships, and deploy only what clears 95%. Seven months, 333,731 messages scored, published whole." url: https://warminboxes.com/research/inbox-placement-log breadcrumb: "Home > Deliverability Hub > Placement Test Log" --- [WarmInboxes.com](https://warminboxes.com/) [Offer](https://warminboxes.com/offer) [Free Leads](https://warminboxes.com/leads) [Free Tools](https://warminboxes.com/deliverability-tools) [Blog](https://warminboxes.com/blog) [Reviews](https://warminboxes.com/reviews) [Home](https://warminboxes.com/) › [Deliverability Hub](https://warminboxes.com/deliverability-hub) › Placement Test Log [Deliverability Hub](https://warminboxes.com/deliverability-hub) Placement Test Log Placement test log # Every placement test we ran on prewarmed inboxes We build a new batch of prewarmed domains and inboxes every month and seed-test it before any of it reaches a customer. 7 tests so far, 379,590 messages sent and 333,731 scored, published whole. 7 monthly tests 333,731 messages landed and scored 95.45% reached the primary inbox 88.41% worst month (Jul) Nothing is deployed below 95%. The test scores every inbox and domain in the month’s batch, one at a time. The ones that clear 95% inbox placement go into the pool; the ones that do not are thrown out. Each figure below is the whole batch’s average *before* that filtering, so a low month never means weak stock shipped — it means more of that month’s batch was discarded. So read this as a barometer, not a scorecard. Each month’s figure is a fresh batch of infrastructure meeting the receivers as they were that month, scored before anything is filtered out, which makes the series a fairly direct read on how hard inboxing was getting. It sat near 99% through spring, fell to 88.41% by July 2026, and is back to 95.49% in September 2026. Anyone sending cold email through 2026 lived through the same summer; most of them are not publishing what it did to them. The damage was not spread evenly, and that is the useful part. Google-sent mail held throughout — Google into Google is the only route measured in every single test and it never dropped below 93.83%. Microsoft into Google is the one that broke: 100% in Mar, 0.22% at the bottom, 86.35% once it came back. The log ## Month by month Inbox and spam are shares of what the seed list *received*, not of what was sent. Where received is well below sent, part of the list did not accept the message at all, which is a different failure from landing in spam and is kept visible rather than folded in. Volume varies a lot between tests, so read the rate next to the count beside it. | Test | Sent | Received | Inbox | Spam | Inbox rate | | --- | --- | --- | --- | --- | --- | | March 2026 | 38,479 | 38,366 | 38,042 | 324 | 99.16% | | April 2026 | 67,681 | 66,894 | 66,353 | 541 | 99.19% | | May 2026 | 78,907 | 57,195 | 56,505 | 690 | 98.79% | | June 2026 | 50,321 | 36,426 | 32,882 | 3,544 | 90.27% | | July 2026 | 62,928 | 58,169 | 51,428 | 6,741 | 88.41% | | August 2026 | 3,004 | 2,983 | 2,955 | 28 | 99.06% | | September 2026 | 78,270 | 73,698 | 70,376 | 3,322 | 95.49% | | All 7 tests | 379,590 | 333,731 | 318,541 | 15,190 | 95.45% | Inbox rate by month 99.2% Mar 38k 99.2% Apr 67k 98.8% May 57k 90.3% Jun 36k 88.4% Jul 58k 99.1% Aug 3k 95.5% Sep 74k Scaled from 80% so the movement is visible — a zero baseline would draw seven near-identical columns. The figure under each month is how many messages it scored: Aug ran 2,983, 0.9% of the total, so its 99.06% is the least load-bearing number on this page. By route ## Which sender reached which inbox Inbox percentage for each sender-to-recipient pair, month by month. These percentages carry no volume. The platform reports placement per route without saying how many messages went down each one. June's Google into Other reads 0% while June overall reads 90.27%, which is only possible if that route is tiny. A dash means the test did not exercise that pair at all, which is a different thing from zero. Read this table for direction and the one above for magnitude, and do not multiply one by the other. | Sender → Recipient | Mar | Apr | May | Jun | Jul | Aug | Sep | Worst | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Google → Google | 98.42% | 98.51% | 96.56% | 99.42% | 93.83% | 98.89% | 97.30% | 93.83% | | Google → Microsoft | 99.90% | 100% | 99.91% | 99.81% | 82.24% | 99.79% | 92.17% | 82.24% | | Google → Other | 98.39% | 98.36% | 96.74% | 0% | 85.10% | 89.74% | — | 0.00% | | Microsoft → Google | 100% | 80.92% | 95.69% | 0.49% | 0.22% | — | 86.35% | 0.22% | | Microsoft → Microsoft | 100% | 100% | 100% | 75.50% | 99.80% | — | 100% | 75.50% | | Microsoft → Other | 100% | 78.26% | 86.67% | 0% | 0% | — | — | 0.00% | August 2026: We built no new Azure prewarmed in August, so the batch had no Microsoft-sender inboxes in it. The three Microsoft rows are absent, not zero. Google senders were the resilient ones. Google into Google is the only route exercised in all 7 tests, and it never dropped below 93.83% — including in the two months everything else did. Microsoft into Google is where it broke. 100% in Mar, 86.35% by Sep. Microsoft senders kept reaching Microsoft recipients almost perfectly over the same period, so this is not a problem with the sending infrastructure — it is Google deciding differently about who it accepts mail from. That is the whole case for routing by recipient rather than sending everything from one place, and we did not set out to prove it here. It fell out of a seed test designed only to measure placement. Method and limits ## How to read this - Tested before deployment, not after. Each test runs on a month’s new batch of prewarmed domains and inboxes before any of it is sold. Every inbox is scored individually and joins the pool only if it clears 95%, so these figures are acceptance scores for a whole batch, not a report on live customer sending. - Seed tests, not campaigns. These measure where a message lands in a panel of monitored inboxes. They do not measure reply rate, and a high placement rate is not a promise of replies. - Prewarmed infrastructure only. Every test ran on prewarmed inboxes. Fresh inboxes and bought-in stock behave differently and are not in this log. - Received, not sent, is the denominator. In May and June the seed list accepted about 72% of what was sent. That is a separate failure from spam placement and it is shown rather than absorbed. - Category is zero throughout. The platform reports a Promotions-style category column and it read zero in every test, so it is left out of the tables rather than printed as a column of zeroes. - A live log. A new batch is built and tested every month, and the result is added here when it completes. The series is the closest read we have on the state of inboxing month to month. - Seven months is a trend, not a law. Placement moves with what the receivers are doing, and this is a short window on one fleet. Proof ## The results screens themselves Every number in the tables above is read off one of these. All 7 tests are pictured, in order, including the two months that went badly. ### Prewarmed March 2026 38,479 sent · 38,366 received · 38,042 inbox (99.16%) · 324 spam (0.84%) · category 0 ![Prewarmed March 2026 results screen: 38,479 sent, 38,366 received, 38,042 inbox at 99.16%, 324 spam, with inbox placement broken down by sender and recipient platform.]() ### Prewarmed April Test 67,681 sent · 66,894 received · 66,353 inbox (99.19%) · 541 spam (0.81%) · category 0 ![Prewarmed April Test results screen: 67,681 sent, 66,894 received, 66,353 inbox at 99.19%, 541 spam, with inbox placement broken down by sender and recipient platform.]() ### Prewarmed May Test 78,907 sent · 57,195 received · 56,505 inbox (98.79%) · 690 spam (1.21%) · category 0 ![Prewarmed May Test results screen: 78,907 sent, 57,195 received, 56,505 inbox at 98.79%, 690 spam, with inbox placement broken down by sender and recipient platform.]() ### Prewarmed June Test 50,321 sent · 36,426 received · 32,882 inbox (90.27%) · 3,544 spam (9.73%) · category 0 ![Prewarmed June Test results screen: 50,321 sent, 36,426 received, 32,882 inbox at 90.27%, 3,544 spam, with inbox placement broken down by sender and recipient platform.]() ### Prewarmed July Test 62,928 sent · 58,169 received · 51,428 inbox (88.41%) · 6,741 spam (11.59%) · category 0 ![Prewarmed July Test results screen: 62,928 sent, 58,169 received, 51,428 inbox at 88.41%, 6,741 spam, with inbox placement broken down by sender and recipient platform.]() ### August Prewarmed 3,004 sent · 2,983 received · 2,955 inbox (99.06%) · 28 spam (0.94%) · category 0 ![August Prewarmed results screen: 3,004 sent, 2,983 received, 2,955 inbox at 99.06%, 28 spam, with inbox placement broken down by sender and recipient platform.]() ### Prewarmed September 78,270 sent · 73,698 received · 70,376 inbox (95.49%) · 3,322 spam (4.51%) · category 0 ![Prewarmed September results screen: 78,270 sent, 73,698 received, 70,376 inbox at 95.49%, 3,322 spam, with inbox placement broken down by sender and recipient platform.]() These are our own tests on our own fleet, run from the account that sends them. Nothing is cropped out of the figures: the sent and received counts, the spam column and the per-route breakdown are all on the screen as captured. ## Route your sending the way the data says Google recipients from Google inboxes is the lesson of 7 months of this. The segmenter sorts a list by recipient platform so you can buy the right mix, and it is free. [Segment a list by ESP](https://warminboxes.com/esp-segmenter)[Get prewarmed inboxes](https://app.warminboxes.com) [Back to the Deliverability Hub](https://warminboxes.com/deliverability-hub) ## Prewarmed & Fresh Inboxes Google, Microsoft 365 and Azure inboxes with free prewarmed domains and DNS configured before you log in. Prewarmed inboxes send the same day you order. 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