Cold email mailbox calculator

How many mailboxes and domains your volume needs, what they cost, and when you can start sending.

To send that volume safely you need

0mailboxes
across
0domains
0emails per day
0emails per month
$0lowest monthly cost
Week 3first cold send

What that costs

Two providers we use and recommend, priced for the mailbox count above.

Two weeks of warmup first

Mailboxes cannot send cold email the day you buy them. Budget two weeks before the campaign goes live.

Assumes 15 emails per mailbox per day after warmup, 3 mailboxes per domain, and 22 sending days a month. Fifteen a day is the safe ceiling on Google and Microsoft mailboxes in 2026. Keep warmup running permanently, not only for the first two weeks.

Buying the mailboxes is the easy part.

Volume only works if the list and the timing are right. We build the signal layer that decides who gets the email and when.

Book 30 minutes

Running a real campaign?

Leave your work email and we will send these numbers over plus a short deliverability checklist, and take a look at your setup if you want a second pair of eyes. No pitch unless you ask.

Thanks, that is with us. We will be in touch shortly.

How it works

How the cold email mailbox calculator works

Tell it your target send volume and this free calculator works out how many mailboxes and domains you need, what they cost, and when you can start sending after warmup.

1

Enter your daily or monthly volume

How many cold emails you want to send. That single number drives everything else the calculator works out.

2

We size the setup

It works out how many mailboxes you need at a safe send rate, how many domains to spread them across, and the monthly cost at typical provider pricing.

3

See your warmup runway

It tells you how long to warm the inboxes before you send at full volume, so you do not torch fresh domains on day one.

The thinking

How many mailboxes do you need for cold email?

The rule of thumb: keep each mailbox to about 15 cold emails a day on a warmed domain, and no more than 3 mailboxes per domain. With roughly 15 warmup emails on top of that, a domain sends around 90 emails a day, which stays under the 100 a day ceiling Google and Outlook expect. So the number of mailboxes you need is your daily cold volume divided by 15, then grouped 3 to a domain. This calculator does that math for you.

Volume is a deliverability decision, not just a cost one. Sending 1,000 cold emails a day from a handful of inboxes will burn them. Spread the same 1,000 across enough mailboxes and domains, about 15 cold sends per inbox and 3 inboxes per domain, and each one stays under the radar. The difference is warmup and spread, and it is the single most common reason cold email setups fail before the copy ever gets read.

It also shows the part people forget: warmup time and monthly cost. New mailboxes need about two weeks of gradual warmup before they carry real volume, and you keep a light warmup running after that alongside the 15 cold sends. The provider bill scales with inbox count, so knowing both up front stops you promising a launch date your infrastructure cannot hit.

Who it is for

Who uses a mailbox calculator

📈

Teams scaling cold email

Size the infrastructure before you buy it, not after inboxes start bouncing and replies dry up.

🤝

Agencies onboarding clients

Quote the right domain and mailbox setup, and the real warmup runway, on the very first call.

🧭

First time cold email setups

Avoid the classic mistake of blasting too much volume from too few inboxes and killing the domain.

FAQ

Cold email volume questions people actually search

How many emails can you send per day per domain? +
No more than about 100 total emails per domain per day on Google and Outlook mailboxes. Best practice is 3 mailboxes per domain, each sending roughly 15 cold emails plus 15 warmup emails, which lands around 90 a day per domain and stays under the cap. Scale by adding domains, not by pushing a single domain past 100.
How many mailboxes do you need for cold email? +
Divide your target daily cold volume by about 15 sends per mailbox. To send 300 cold emails a day you need roughly 20 mailboxes, spread 3 to a domain, so about 7 domains. This calculator does the math and tells you the domains too.
How many domains do you need for cold email? +
Keep it to 3 mailboxes per domain, so divide your mailbox count by three. More domains means more resilience: if one gets flagged, the rest keep sending. The calculator sizes this from your volume.
How long does mailbox warmup take? +
Plan for about two weeks before a new mailbox sends at full volume, and keep a light warmup running after that. Warmup ramps sending gradually so providers see a normal pattern rather than a cold domain suddenly blasting. Skipping it is the fastest way to kill a fresh domain.
How much do cold email mailboxes cost? +
It depends on the provider, but typical cold email inboxes run a few dollars each per month, plus the domain registration. The calculator estimates the monthly cost from the number of mailboxes your volume needs so you can budget before you buy.
Is this mailbox calculator free? +
Yes. No sign up and no card. Enter your numbers and get the full setup, mailboxes, domains, cost and warmup time, instantly.
Want us to build the sending infrastructure?

Book 30 minutes and we will map the mailboxes, domains and warmup plan your target volume actually needs.

Book 30 minutes