What is a domain and inbox plan?
A domain and inbox plan turns a sending volume into infrastructure: how many inboxes share the daily emails, how many domains hold those inboxes, and how many weeks a warm-up ramp takes before every inbox sends its full share. Cold email is spread this way so that no single inbox or domain carries the whole volume.
Reading the result
The planner divides your daily emails by what you plan to send from one inbox and rounds up, then divides the inboxes by how many you put on a domain. The ramp table shows each week of warm-up: the volume per inbox, the total across inboxes and how much of your target that covers. Below it, your per-inbox number is set against the ceilings Google and Microsoft publish, quoted from their own pages.
Where plans usually go wrong
Treating a provider limit as a target
Google publishes 2,000 messages a day per Workspace user, and Microsoft 10,000 recipients a day per mailbox. Those are the points where the provider stops the account. They say nothing about what lands in the inbox, so the number per inbox has to come from your own judgement.
Skipping the ramp
A new inbox on a new domain has no sending history for receivers to judge it by, which is why senders raise volume gradually. The pace is your choice, and the table shows what it costs in weeks.
Forgetting the trial limit
Google applies a lower daily limit, 500 messages, to Workspace trial accounts. A plan sized for paid accounts runs out early on a trial.
Counting a month as thirty sending days
If you send on working days only, a monthly target is shared across fewer days than the calendar shows, and each day carries more. Set the sending days to the ones you actually use.