Free tool / cold email infrastructure
Cold email infrastructure calculator
This cold email infrastructure calculator turns one number, how many cold emails you want to send a day, into the domains, inboxes, and mailbox orders to buy. Sending 10,000 a day on a 60/40 Microsoft and Google split takes 163 domains and 1,587 inboxes. Change the inputs and the plan updates.
Warm every inbox for 14 days before the first cold send.
| The math | Microsoft | |
|---|---|---|
| Daily sends carried | 4,000 | 6,000 |
| Sends per inbox per day | 15 | 5 |
| Inboxes needed | 267 | 1,200 |
| Orders to buy | 3 × 100 | 13 × 99 |
| Domains | 150 | 13 |
| Daily capacity built | 4,500 | 6,435 |
Every number here is division, not judgment
There are only two limits that matter. A Microsoft inbox sends 5 cold emails a day, and one domain covers a whole tenant of 99 inboxes. A Google inbox sends 10 to 15, and one domain covers only 2 inboxes. Everything else falls out of those two rows. The full reasoning behind the limits is in how many cold emails to send per day.
The provider split is a cost decision, not a deliverability one
Slide the Microsoft share to zero and watch the domain count climb. Google inboxes send more each, but they need a domain for every two, and domains are the line item that compounds. Microsoft sends less per inbox and needs far fewer domains. We run about 60/40 Microsoft to Google for exactly that reason. The cost side of the build, including why we buy .info domains at about $2.57 a year instead of $10 to $12 for a .com, is in the cheap infrastructure breakdown.
What the calculator cannot tell you
It sizes capacity. It does not tell you whether the list or the offer deserves the volume. More infrastructure behind a weak offer just finds out faster that the offer is weak. If you are still deciding whether cold email is the right channel at all, the cold email vs paid ads ROI calculator compares cost per booked call on both. Set up the sending side properly first with our cold email infrastructure guide, then spend the capacity on a list that is actually worth emailing. Microsoft's own Exchange Online sending limits and Google's email sender guidelines are the hard ceilings underneath all of this.
FAQ
How many domains do I need to send 10,000 cold emails a day?
About 163 on a 60% Microsoft, 40% Google build. Google runs 2 inboxes per domain, so its 4,000 sends a day need 150 domains. Microsoft runs one domain per tenant of 99 inboxes, so its 6,000 need only 13. The domain count, not the inbox count, is what makes one provider mix cheaper than another.
How many cold emails can one inbox send per day?
It depends on the provider. Microsoft inboxes start and stay at 5 a day. Google inboxes carry 10 to 15. Pushing either harder does not add volume, it burns the inbox. Volume comes from more inboxes across more domains.
Why does the calculator buy more inboxes than I need?
Mailboxes come in orders: 100 per Google order and 99 per Microsoft tenant. The calculator rounds up to whole orders, so the build always carries a little more than your target. That spare capacity is useful while a few inboxes are resting or being replaced.
How long before I can send from new infrastructure?
14 days. The inboxes spend that window emailing each other so they look like real accounts. Sending before warmup finishes is the fastest way to burn every domain you just bought.
If you would rather not buy, name, and warm 163 domains yourself, that is what we do, on infrastructure you own at the end.
