What warm-up does and why it takes weeks
A new mailbox has no sending history. Receiving servers decide how to treat it by watching early behaviour: how much it sends, how quickly volume grows, and whether anyone replies. Warm-up is the process of building that history deliberately, starting with a few emails a day to inboxes that open, reply and move messages out of spam, then raising volume gradually until the mailbox can carry campaign traffic.
The schedule matters more than the total. Ten emails a day for two weeks looks like a person settling into a job; fifty on day two looks like a compromised account. That is why the calculator checks how many days the ramp takes and flags anything that reaches target in under ten days.
Choosing a starting point and ramp
Brand-new Google Workspace mailboxes on fresh domains should open in low single digits and increase by a couple of emails a day. Mailboxes on a domain that already has clean history can start a little higher. Percentage ramps start very slowly and then accelerate, which suits cautious operators; linear ramps are easier to reason about and to configure in most tools.
- Start at 3 to 5 sends a day on new domains, and keep the first week flat if the domain was registered this month.
- Add 2 to 3 a day, or 20 to 25% a day, and hold at the target rather than continuing to climb.
- Aim for a warm-up reply rate of 30 to 40% so the traffic reads as real conversation.
- Keep a reduced warm-up volume running after launch; do not switch it off the day campaigns begin.
Day 1 5 per mailbox
Day 5 13 per mailbox
Day 10 23 per mailbox
Day 14 30 per mailbox (ready)
10 mailboxes, +2 a day: about 2,400 warm-up emails before launchReading the verdict and warnings
The tool judges the ramp on days to ready. Under seven days is marked as a fail because there is no realistic way for a receiving server to trust that much growth. Seven to nine days is a warning, workable only on domains with existing reputation. Ten to twenty-eight days is the healthy range for most cold email setups, and anything longer is safe but slow.
You will also see a warning when the starting volume is above ten a day or the target is above thirty. Both are common causes of early blocks. If you need more total volume, add mailboxes rather than pushing each one harder, and use the mailbox calculator to size the fleet.
Warm-up versus pre-warmed mailboxes
Every schedule the calculator produces is time you spend waiting before campaigns start. Agencies onboarding a client, or teams replacing burned domains mid-quarter, often cannot afford a three-week gap. Pre-warmed mailboxes shift that ramp to before you buy them, so they arrive with history and only need a short settling period. InboxOne provisions Google Workspace mailboxes that come pre-warmed with authentication already configured, which removes most of the schedule above from your critical path.
