Cold email inbox calculator

Enter how many emails you want to send a month and get the inboxes, domains, warmup time and cost you need.

Updates as you dragDefaults: 25 a day per inbox, 3 per domain, 20 sending daysAdjust assumptions

You need 60 inboxes on 20 domains.

That is 1,500 emails a sending day, 25 per inbox, 3 inboxes per domain, 20 sending days. Full volume after a 2-week warmup.

A sending day

1,500

20 sending days a month.

Per inbox

25 a day

Cold sends, once warmed.

Per domain

3 inboxes

One bad inbox cannot sink every domain.

Warmup

2 weeks

Cold sends start in week 2.

The fleet

20 domains, 60 inboxes

Every square is one inbox. Drag the slider and watch it fill.

InboxSpare slot

getyourbrand.com

tryyourbrand.com

yourbrandhq.com

useyourbrand.com

yourbrandmail.com

joinyourbrand.com

yourbrandteam.com

goyourbrand.com

meetyourbrand.com

helloyourbrand.com

getyourbrand.co

tryyourbrand.co

yourbrandhq.co

useyourbrand.co

yourbrandmail.co

joinyourbrand.co

yourbrandteam.co

goyourbrand.co

meetyourbrand.co

helloyourbrand.co

Domain names are placeholders. The domain generator finds available siblings of yourbrand.com.

Warmup timeline

Cold sends a day from the whole fleet, by week

Week 1

warmup only

Week 2

780 a day

Week 3 on

1,500 a day

Full volume from

Day 14

If you buy today.

Cold sent during warmup

5,460

Real cold emails before full volume.

Buy all 60 at once. Warming in batches delays full volume by the length of the ramp for every batch, and the cost is the same. Warmup traffic runs alongside from day one.

Monthly cost

Inboxes and domains for the fleet above.

Google Workspace

$445a month

60 inboxes x $7$420

20 domains x $15 a year$25

Warmup and setupExtra, you set it up

Microsoft 365

$385a month

60 inboxes x $6$360

20 domains x $15 a year$25

Warmup and setupExtra, you set it up

Ken (Google Workspace)Warmup built in

$266.67a month

60 inboxes x 200 credits ($4)$240

20 domains x $16 a year (registrar $15 + 3%, rounded up)$26.67

PlanOn top of the Platform plan

Google and Microsoft are vendor list prices for annual plans, domains at $15 a year. Ken prices come from the Ken rate card: an inbox is 200 credits ($4) a month and a domain is the registrar price plus 3%, rounded up to the dollar. Ken is $178.33 a month less than Google for this fleet, before the Platform plan. Prewarmed inboxes add 300 credits ($6) once per inbox.

Adjust assumptions25 a day per inbox · 3 per domain · 20 sending days · $15 a domain

Emails per inbox per day

Most senders stay under 50 a day.

Inboxes per domain

2 or 3 keeps the blast radius small.

Sending days a month

20 is weekdays only.

Domain price a year ($)

Registrar price for a .com.

Your brand, for the example names

The shopping list

Everything the fleet above needs. Ken runs it for you, or take the list anywhere.

Google Workspace inboxes

Sending domains

SPF, DKIM and DMARC on every domain

Required

Warmup, 2 weeks

Before full volume

On Ken, a month

$266.67

Never send cold email from your primary domain. Buy separate sending domains for outbound and keep your main domain for normal mail, so a spam complaint cannot touch it.

Buy these in Ken

The Ken link opens sign-up with 1,000 free credits and no card. Paste the list when you add inboxes.

Warmup calculator: the day-by-day ramp

Then

Sending domain generator: names that are free now

Send me the shopping list

The fleet, the warmup weeks, the cost table for each provider and a saved link that stays live for 90 days.

Shopping list as HTMLCost table for Google, Microsoft and KenLink to this plan, live for 90 days

Put Ken on the rest of your outbound

Inboxes, warmup, leads and copy in one place. Ken runs these checks on every inbox it manages.

Start free - 1,000 credits, no card

What the inbox calculator does

Enter how many cold emails you want to send a month. The calculator works out how many inboxes and domains that takes, how many emails each inbox sends a day, how many weeks of warmup come before full volume, and what the setup costs on each type of provider.

The math

Monthly volume divided by sending days gives the daily volume. Daily volume divided by the cold sends you allow per inbox gives the inbox count, rounded up. Inboxes divided by inboxes per domain gives the domain count, also rounded up.

An example with 25 sends per inbox a day and 3 inboxes per domain: 20,000 emails a month over 20 weekdays is 1,000 a day, which takes 40 inboxes on 14 domains. Change any assumption and the numbers follow.

Count follow-ups in the volume. A four-step sequence to 5,000 new leads is 20,000 emails, not 5,000.

Why the per-inbox number is so low

Google Workspace lets a user send up to 2,000 messages a day, and Microsoft 365 allows 10,000 recipients a day per mailbox. Those are ceilings for normal mail, not safe volumes for cold email. Cold mail gets fewer replies and more spam reports than mail people expect, and filters judge each inbox and domain on that ratio.

So outbound teams keep each inbox to a few dozen cold sends a day and spread volume across more inboxes and domains. If one domain picks up a bad reputation, the rest keep sending.

Why it matters for cold email

Infrastructure is the first thing to get right and the slowest to fix. New inboxes need two to four weeks of warmup before they carry full volume, so buying too few means a month of waiting when you need more. Buy the full set at once and warm it together.

Never put cold email on your main domain. Sending domains should be close variants of your brand, with their websites redirecting to your main site. Ken sells inboxes on separate sending domains, with prewarmed inboxes as an option for teams that can't wait out warmup.

Questions

How many inboxes do I need for cold email?

Divide your daily volume, follow-ups included, by the cold sends you allow per inbox, and round up. At 25 a day per inbox, 1,000 emails a day takes 40 inboxes.

How many inboxes should I put on one domain?

A common setup is 2 or 3. More inboxes per domain means fewer domains to buy, but when that domain's reputation drops, every inbox on it goes down together.

How many cold emails can one inbox send a day?

A few dozen once the inbox is warmed up. Google's limit of 2,000 a day is a ceiling for normal mail, not a target. Cold email is judged on replies and spam reports, and every inbox carries its own reputation.

Google Workspace or Microsoft 365 for cold email?

Both work, and a mix spreads the risk: one provider tightening its filters doesn't stop all your sending. Some teams also match the sending provider to each prospect's provider. The ESP checker shows that split for a list.

How long until new inboxes can send at full volume?

Two to four weeks of warmup, starting with a few emails a day and rising step by step. The warmup calculator gives the day-by-day ramp. Prewarmed inboxes skip most of the wait.