I tested 14 day versus 30 day warmup on 20 identical inboxes. Here are the actual GlockApps inbox placement numbers
warmup_test_james · 2026-08-04 · 1,050 views
Everyone recommends 30 days of warmup. I wanted real data instead of received wisdom. So I ran a controlled test.
I bought 20 identical PuzzleInbox Google Workspace inboxes in January. Same domains, same DNS setup, same Instantly warmup settings. Ten inboxes I warmed for 14 days before starting cold sends. Ten I warmed for 30 days.
After two weeks of cold sending I ran GlockApps inbox placement tests on all 20 inboxes. Here are the actual numbers.
14-day warmup group: 82 percent inbox placement on Gmail. 91 percent on Microsoft. Reply rate in first two weeks of sending: 2.8 percent.
30-day warmup group: 87 percent inbox placement on Gmail. 93 percent on Microsoft. Reply rate in first two weeks: 3.1 percent.
Five percentage points of inbox placement. About 0.3 percent higher reply rate. Is it meaningful? Yes. Is it worth two extra weeks of zero revenue? For most people, probably not.
My conclusion: 14 days is the genuine minimum. You will see a small deliverability gap versus 30 days in the first month. By month two the gap closes as the inbox builds its own sending history with real replies coming in.
If you are an agency onboarding a new client who needs results fast, 14 days with a careful ramp-up is defensible. If you are building infrastructure meant to run for 12 months, 21 to 30 days gives you a cleaner start with less early-campaign risk.
The one line I will not cross: starting cold sends before 14 days no matter how impatient I am or how impatient the client is. Below 14 days the inbox placement drop is not small. It is catastrophic. I have seen inboxes started at 7 days end up in the spam folder permanently. PuzzleInbox recommends 14 days as the hard minimum and that recommendation holds up in the data.