How many inboxes do you need for cold email?
Take the number of cold emails you want to send per working day, follow-ups included, and divide by 15 to 30. That is the range inbox sellers publish for one inbox: Maildoso and Premium Inboxes say 15, the Forge products (Mailforge, Infraforge, Primeforge) recommend 30, and Puzzle Inbox enforces 12 on Google inboxes in its terms.
So 500 emails a day needs 17 to 34 inboxes, and 1,000 a day needs 34 to 67. At three inboxes a domain, the conservative end needs 12 and 23 domains. At the cheapest published per-inbox price for Google seats on monthly billing ($3.00), 67 inboxes and 23 domains cost about $230 a month; bought directly from Google at $8.40 a seat, the inboxes alone are $563.
What counts as a send
Every message an inbox sends counts against its daily limit: the first email and every follow-up. A sequence of one email and two follow-ups sends three emails per prospect. Warm-up messages usually count separately; Puzzle Inbox's terms set 12 cold plus 12 warm-up a day on Google, Maildoso allows 15 cold plus 80 warm-up.
So start from prospects, not emails. 2,000 new prospects a month on a three-step sequence is 6,000 emails; over 22 working days that is 273 a day, or 10 inboxes at 30 a day and 19 at 15. The same 2,000 prospects on a five-step sequence is 455 a day and up to 31 inboxes.
| New prospects a month | Steps in the sequence | Emails a month | Emails a working day | Inboxes at 30 a day | Inboxes at 15 a day |
|---|---|---|---|---|---|
| 1,000 | 3 | 3,000 | 137 | 5 | 10 |
| 2,000 | 3 | 6,000 | 273 | 10 | 19 |
| 2,000 | 5 | 10,000 | 455 | 16 | 31 |
| 5,000 | 4 | 20,000 | 910 | 31 | 61 |
| 10,000 | 3 | 30,000 | 1,364 | 46 | 91 |
Why the limit is per inbox
Receivers judge senders by domain and by address. Google requires anyone sending more than 5,000 messages a day to Gmail accounts to authenticate with SPF, DKIM and DMARC and to keep spam complaints under 0.10%, never reaching 0.30%. Microsoft applies similar rules to Outlook.com for domains sending over 5,000 a day, and Yahoo declines to state any threshold at all.
Spreading volume across many inboxes keeps each address and domain low, and it limits the damage when one is flagged: a burned inbox takes its 15 to 30 daily sends with it, not the whole campaign. It does not change how recipients react. A message people mark as spam is marked as spam from any inbox.
Inboxes, domains and cost at eight sending volumes
Inboxes at 30 and at 15 cold emails a day each, domains at three inboxes per domain on the 15-a-day count, and the monthly cost at $3.00 an inbox (InboxKit's monthly rate, the lowest no-minimum price for Google seats) plus $15 a domain a year. The last column is Google Workspace bought directly at $8.40 a seat, inboxes only. Computed from published rates, read 29 October 2026.
| Cold emails a day | Inboxes at 30 a day | Inboxes at 15 a day | Domains | Monthly cost, reseller | Monthly cost, Google direct | Emails a month |
|---|---|---|---|---|---|---|
| 100 | 4 | 7 | 3 | $25 | $59 | 2,200 |
| 250 | 9 | 17 | 6 | $58 | $143 | 5,500 |
| 500 | 17 | 34 | 12 | $117 | $286 | 11,000 |
| 1,000 | 34 | 67 | 23 | $230 | $563 | 22,000 |
| 2,000 | 67 | 134 | 45 | $458 | $1,126 | 44,000 |
| 5,000 | 167 | 334 | 112 | $1,142 | $2,806 | 110,000 |
| 10,000 | 334 | 667 | 223 | $2,280 | $5,603 | 220,000 |
| 20,000 | 667 | 1,334 | 445 | $4,558 | $11,206 | 440,000 |
Above about 300 inboxes, per-inbox pricing stops being the cheap way to buy. Maildoso sells 300 inboxes on its own servers for $225 a month and 1,000 for $499 on its page ($500 at checkout); Inframail sells a plan it recommends for up to 400 Microsoft-backed inboxes at $147 per 28-day cycle, $159.25 a calendar month. The inbox provider census has all twelve sellers at 10, 30, 100 and 300 inboxes.
The daily limit each seller sets
The divisor is not yours to choose freely if a seller enforces one. These are the figures sellers publish for one inbox, with what they say about inboxes per domain.
| Seller | Cold emails per inbox per day | Inboxes per domain | Where it is stated | Enforced? |
|---|---|---|---|---|
| Puzzle Inbox, Google | 12 (plus 12 warm-up) | 3 | Terms of service, section 3 | Yes: suspension without refund |
| Puzzle Inbox, Outlook | 3 (plus 3 warm-up) | Up to 100 | Terms of service, section 3 | Yes |
| Maildoso | Up to 15 (ramp from 1) | Up to 99, 8 recommended | Pricing FAQ and terms | Stated as a limit |
| Premium Inboxes | 15 | 3 | Pricing page | Recommendation |
| Litemail | 20 (calculator default) | 5 (calculator default) | Homepage calculator | Recommendation |
| Mailreef | 25 (calculator), 50 maximum | 3 maximum | Pricing page | Recommendation |
| Mailforge, Infraforge, Primeforge | 30 recommended, 100 maximum | 2 to 3 recommended | Pricing FAQ | Recommendation |
| Inframail | About 10 (slider), 50 'safe sending' | 5 (slider) | Homepage | Recommendation |
Four sellers land between 12 and 20, three recommend 30. The cheapest way to read this table: if you are buying from a seller that enforces a limit, use its number; otherwise 15 is the conservative end and 30 the aggressive one, and the difference doubles your inbox count.
How many domains you need
Divide inboxes by inboxes per domain. Three per domain is the most common figure in the table above (Puzzle Inbox's Google plans, Premium Inboxes, Mailreef's maximum), so 34 inboxes need 12 domains and 67 need 23. At five per domain, which Litemail's and Inframail's calculators assume, 67 inboxes need 14.
Domains cost $14 to $15 a year at the sellers that publish a price (Mailforge's .com at $14, Litemail and Maildoso at $15), or about $1.25 a month each. At 23 domains that is $28.75 a month, small next to the inboxes, but it is the part you should own: a domain registered in your name keeps its sending history if you change seller, and one registered by the seller may not.
The cap Microsoft puts on a new tenant
Microsoft limits how many external recipients a whole Exchange Online tenant can reach per day: 500 × (licences^0.7) + 9,500. For a 67-inbox tenant that is 18,989 a day, far above 67 × 30 = 2,010. But a tenant less than 31 days old gets 10% of its quota, and 25% between days 31 and 60.
Ten percent of 18,989 is about 1,899 a day across the tenant, or 28 an inbox: below a 30-a-day plan in the first month, before any warm-up traffic. A 30-inbox tenant gets about 1,490 a day, roughly 50 an inbox. If you buy Microsoft inboxes on a fresh tenant and plan for 30 a day, the first month's volume is capped by Microsoft, not by your seller. Microsoft's trial tenants are lower still; its own two pages give 500 and 5,000 external recipients a day.
Google's equivalent does not bind at cold email volumes. Trial accounts are limited to 500 messages a day per user until the domain has paid $100, and 'up to 75 days' after that, and paid accounts to 2,000 a day. Both are far above 30.
Buy inboxes before you need them
A new inbox does not send its full daily limit on day one. Maildoso's terms tell buyers to 'gradually increase volume from 1 email per day to a maximum of 15'. Puzzle Inbox's pages give warm-up as 14 days on one page and 14 to 100 days on another. A practitioner on Hacker News described the norm as 'warming email accounts up for 2 weeks' before sending. Microsoft's quota reaches 100% only after 60 days.
So the count in the tables is the count you need warm, which means ordering two weeks or more ahead of the volume. Pre-warmed inboxes skip that wait at a price: Litemail's pre-warmed inboxes are $4.98 to $7.80 an inbox against $2.83 to $3.70 for fresh ones, and Primeforge's are $9 against $4.50, about double.
Spare inboxes for the ones that get burned
Inboxes get flagged and replaced. Premium Inboxes includes unlimited replacement inboxes; Maildoso's terms provide up to 4 replacement domains a year if deliverability falls; Puzzle Inbox gives no refund for any suspension. Whatever the seller, a burned inbox needs a warm one waiting, which means carrying some spare capacity. No seller publishes how often its inboxes are replaced, so there is no measured figure for how many spares to hold.
How to check your inbox count is right
- Count follow-ups. Multiply new prospects by sequence steps before dividing by working days.
- Use your seller's limit if it enforces one. Puzzle Inbox's 12 a day is in its terms with suspension attached.
- Watch Google Postmaster Tools for each domain. If the spam rate approaches 0.10%, send less per inbox rather than adding volume.
- On a new Microsoft tenant, divide 10% of the tenant quota by your inbox count before the first send.
- Check the billing cycle before you multiply by price. Inframail and Premium Inboxes bill every 28 days or four weeks, 13 times a year.
How many inboxes for your volume
- Under 250 a day: 9 to 17 inboxes on 3 to 6 domains, $25 to $58 a month from a reseller. At this size the seller's minimum often decides: Zapmail starts at 10 inboxes for $39, Puzzle Inbox at 15.
- 500 to 1,000 a day: 17 to 67 inboxes on 6 to 23 domains, $117 to $230 a month. Buy two weeks ahead of the volume.
- 2,000 to 5,000 a day: 67 to 334 inboxes. Compare flat and bulk plans here: Inframail's $159.25 covers up to 400 inboxes and Maildoso's 300 cost $225.
- 10,000 a day and up: hundreds of inboxes and hundreds of domains. At this point the question is less inbox count than whether the list and offer can sustain that volume without complaints passing 0.10%.
Inboxes or a bigger list?
More inboxes let you send more email; they do not make anyone reply. Published cold email reply rates run from 0.45% to 10%, as the reply-rate page sets out, so doubling inboxes doubles sends and roughly doubles replies only if the extra prospects are as good as the first ones. If your list is the limit, adding inboxes adds cost and risk and nothing else.
Who answers this question online
The pages ranking for this question on 29 October 2026 were a Reddit thread, an inbox infrastructure seller (InfraSuite), a cold email tool's YouTube channel, a single-purpose calculator site, two more inbox or deliverability sellers, an agency and Smartlead. Most give a formula and stop there. None of them prices the answer, and the ones selling inboxes have a reason to round the divisor down.
What this page does not know
This page does not know the daily volume per inbox at which inbox placement actually falls. That needs identical inboxes on identically warmed domains sending the same message at, say, 10, 20, 30 and 50 a day to a common seed list, measured over weeks. No seller or ranking page publishes that experiment, the 15 to 30 range above is what sellers recommend rather than what anyone has measured, and this page has not run it. Run a small version yourself: split one batch of inboxes across two daily volumes and compare where the messages land.
It also does not know how many inboxes a typical sender loses to suspension or flagging per month, which is the number that would size a spare pool, or how Google counts its 5,000-a-day bulk threshold across many small domains. Keep your own record of replacements from the first month and size spares from that.
The short answer
Inboxes needed = cold emails per day ÷ 15 to 30. Domains = inboxes ÷ 3. For 1,000 a day that is 34 to 67 inboxes and 12 to 23 domains, about $117 to $230 a month from a reseller at $3.00 an inbox. Order them two weeks before you need them, use your seller's own limit if it enforces one, and on a new Microsoft tenant expect fewer than 30 sends an inbox in the first month.