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Free cold email volume and mailbox calculator
Work out how many sending mailboxes and domains your outreach target needs, at 40 messages a day per mailbox and 5 mailboxes per domain. Then see the part every other volume calculator leaves out: whether mailboxes bought on the launch date can warm up fast enough to carry the sequence, or whether the two curves cross in week two.
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In short
- This is a free, ungated cold email volume and mailbox calculator from SmartReach.io. It multiplies the prospects contacted each month by the steps in the sequence, divides by working days and by the messages a day each mailbox may safely send, and groups the result into domains.
- Mailboxes are sized on steady-state volume rather than on the first week. A sequence sends only its first step on day one; steady-state daily volume is the step count times that, and a plan sized on week one is short by exactly that factor.
- SmartReach.io sizes at 40 messages a day per mailbox and 5 mailboxes per domain, and permits up to 200 a day per connected account. Sender reputation attaches to the domain, so the domain count is what decides how much of a programme one filtered week can remove.
- The tool draws two curves on one scale: the volume the sequence demands as its follow-ups stack, and the volume warming mailboxes are allowed to send. Where the first crosses the second, the launch stalls. A new mailbox needs about 19 working days to reach 40 a day.
- Provider limits are far above any rate a cold sender should use. Google Workspace allows 2,000 messages a day and Microsoft 365 allows 10,000 recipients a day at 30 a minute, with Microsoft's own documentation stating Exchange Online is not suited to bulk mail. Microsoft also caps external recipients per tenant, so stacking mailboxes in one tenant does not multiply capacity.
- Raising the per-mailbox rate returns a finding rather than a smaller answer, because it does not create capacity, it converts capacity into deliverability risk.
- The estate is budgeted with a 20% rotation buffer, because mailboxes are suspended, rested and replaced, and priced at market rates for mailboxes and domains, giving a monthly total and a cost per reply. Both prices are editable.
- Across 9 ranking cold email calculators reviewed in September 2026, published rates ran from 3 to 1,000 messages a day per mailbox, warmup from 14 days to 12 weeks, and mailboxes per domain from two to five. SmartReach.io publishes that spread and the reasons behind it rather than presenting one number as settled.
- The calculation runs entirely in the browser. Sending plans are not transmitted, stored or logged, and no account is required.
These are example figures, so the tool is working when you arrive. Type over them.
Nothing is sent anywhere. The calculation runs in this browser tab.
8,000 emails a month · 364 a day at steady state
Mailboxes
10
At 40 a day each, sending about 36. Buy 12 for rotation.
Domains
2
At 5 mailboxes each, carrying 182 a day per domain. Buy 3 to hold the rotation buffer.
A month
$75
12 mailboxes and 3 domains, at the prices in the fields.
This plan needs 10 mailboxes on 2 domains, and cannot launch on the day they are bought. The sequence outruns warmup from working day 1, peaking 134 messages a day short on day 10. Start warming about 19 working days before launch and the two curves never meet.
Worst day is working day 10, 134 messages a day short · clears on day 17. Hover any day for its figures.
Day one sends
91
The first touch only. Steady state is 4× this, reached on day 10.
Warmup to full rate
19
Working days, about 4 weeks. Buy the mailboxes that far ahead.
Cost per reply
$0.09
Infrastructure only. $0.04 per prospect contacted.
Replies a day
36
At 10%, about 12.1 hours a week to answer.
| Week | Tightest day | Sequence wants | Mailboxes allow | Short by |
|---|---|---|---|---|
| Week 1 | Day 4 | 182 a day | 110 a day | 72 a day |
| Week 2 | Day 10 | 364 a day | 230 a day | 134 a day |
| Week 3 | Day 11 | 364 a day | 250 a day | 114 a day |
| Week 4 | Day 16 | 364 a day | 350 a day | 14 a day |
| Week 5 | Day 21 | 364 a day | 400 a day | Covered |
- Read this
Your sequence outruns your warmup in week 1
By working day 1 the sequence wants 91 messages a day and 10 warming mailboxes are allowed 50. The gap peaks at 134 messages a day on day 10 and closes on day 17. Something has to give, and the sender chooses what: start warming the mailboxes 19 working days before launch, feed prospects in more slowly for the first 10 days, widen the gap between steps, or buy mailboxes you will not need at steady state. Sending through it is the one option that is not available, because the mailboxes will not carry it.
- Worth knowing
Day one sends 91 a day, steady state sends 364
Only the first step of the sequence goes out on day one. The second joins it on day 4, the third on day 7, and by working day 10 every step is running against a different cohort at once. Steady state is 4 times day one. Sizing mailboxes on what week one sends is the commonest way to under-provision by exactly that factor, and it is why this plan can look 4x too large for its first fortnight.
- Worth knowing
This plan runs at 91% of its own ceiling
There are 36 messages a day of slack across 10 mailboxes. One mailbox suspended, one domain flagged, or one week where the list lands heavier than planned, and the sequence starts skipping sends rather than slowing down. Sizing to about 80% of capacity is what makes a plan survive its own bad week, and here that is 12 mailboxes rather than 10.
- Note
Budget for 12 mailboxes, not 10
10 carries the volume on a week when nothing goes wrong. Mailboxes are suspended, rested, replaced after a bad patch and re-warmed, and an estate sized exactly to its own steady state skips sends the first time one is lost. A fifth again is what this category converged on and it is the cheapest insurance on this page: 12 mailboxes across 3 domains costs about 75 a month at the prices in the fields above.
- Worth knowing
The replies are 12.1 hours a week of somebody's time
At a 10% reply rate this volume produces about 36 replies a day, or 182 a week. That is the constraint most teams hit before they hit the sending one, and no number of mailboxes moves it. A programme that sends more than it can answer converts interest into silence, which is more expensive than the mailboxes are.
Sizing the estate is the easy half
Running it is the other half: warmup tracked per mailbox, sending spread across every domain, and a sequence that stops the moment somebody replies. SmartReach.io rotates sending across unlimited connected mailboxes and reports volume per mailbox, per domain and per campaign, so a plan drawn on this page is visible against what actually went out. The benchmarks behind the reply figures come from 40M+ emails across 5,000+ campaigns in our State of Cold Email 2026 report.
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What this cold email volume calculator does
This calculator sizes the infrastructure a sending target needs and then tests whether that infrastructure can carry the target in its first month. It multiplies prospects by sequence steps to get monthly volume, divides by working days and by 40 messages a day per mailbox to get mailboxes, and groups those into domains at 5 per domain. Then it draws two curves that no competing calculator draws together: what the sequence demands each day as its follow-ups stack on top of each other, and what mailboxes still in warmup are allowed to send. Where the first crosses the second, the plan stalls, and SmartReach.io names the day it happens and the four things that can be done about it.
The sizing
How many mailboxes and domains do you need?
SmartReach.io sizes at 40 messages a day per mailbox and 5 mailboxes per domain, across 22 working days and a four-step sequence, priced at $6 a mailbox a month and $12 a domain a year. Read the table by the row that matches your list, and note the two columns the category never prints side by side: what the first day sends and what steady state sends. They differ by the step count, and the mailbox column is sized on the second of them. The last two columns are what to actually buy and what it costs, including the 20% of spare mailboxes any rotation needs.
| Prospects a month | Typically | Day one sends | Steady state sends | Mailboxes | Domains | Buy, with buffer | A month |
|---|---|---|---|---|---|---|---|
| 500 | A founder selling | 23 a day | 91 a day | 3 | 1 | 4 | $25 |
| 1,000 | One SDR | 45 a day | 182 a day | 5 | 1 | 6 | $38 |
| 2,500 | A small outbound team | 114 a day | 455 a day | 12 | 3 | 15 | $93 |
| 5,000 | A team of three or four | 227 a day | 909 a day | 23 | 5 | 28 | $174 |
| 10,000 | An agency, or a scaled team | 455 a day | 1,818 a day | 46 | 10 | 56 | $348 |
| 25,000 | A large agency | 1,136 a day | 4,545 a day | 114 | 23 | 137 | $850 |
If you know the meetings you need rather than the prospects you will contact, start at the volume planner on the open rate calculator, which runs the published agency funnel backwards to a send volume. Bring that figure back here to find out what sending it costs.
This page sizes the estate. Buying and configuring it is a separate job: for the how-to, see how to buy secondary domains for cold email, and SmartReach.io also sets up secondary domains and mailboxes on Google, Microsoft 365, Azure or SMTP if you would rather not run the registrar and DNS yourself.
The part the category leaves out
Why your sending volume keeps climbing after launch
A sequence does not send a flat line, and SmartReach.io sizes against the line it actually sends. On day one only the first step goes out. A few working days later the second step joins it, sent to the cohort that started on day one, while a fresh cohort receives the first step. Daily volume climbs one stair at a time until every step of the sequence is running against a different cohort at once. Steady state is the step count times day one. A four-step sequence sends four times as much in its fourth week as in its first, having added no prospects at all, which is why a plan sized on what week one sent is short by exactly a factor of four.
The two ways this goes wrong, and they are opposites
A team that sizes on week one under-buys and starts skipping sends in week three, usually blaming the platform. A team that sizes on the monthly average buys the right number and spends a fortnight watching mailboxes sit idle, concludes it over-bought, and cuts the estate just before the volume arrives that needed it. Both are the same error read from different ends: the average is a destination, and nothing sends the average until the sequence has fully stacked.
The two curves
Can your mailboxes warm up fast enough?
This is the question SmartReach.io built the tool to answer, and no other cold email volume calculator asks it. A new mailbox cannot send at its full rate on the day it is bought: it starts at a handful of messages a day and climbs over about 19 working days, roughly 4 weeks, to reach 40. Meanwhile the sequence is stacking its follow-ups and climbing too. Two curves, one scale, and the plan works or fails on whether they cross. Warmup practice is a convention rather than a published standard, unlike SPF or DMARC, so the ramp modelled here is stated as the assumption it is and is adjustable rather than asserted. For warmup as a subject, rather than as the constraint it puts on a launch date, see the SmartReach.io email warmup guide. This page is the timing.
Start warming before you need the mailboxes
The crossover is a timing problem before it is a capacity one. A mailbox bought 19 working days before launch arrives at full rate on the day the sequence first asks for it, and the two curves never meet. This costs nothing except planning, which is why it is first, and it is the one lever unavailable to a team that discovers the problem after launching.
Widen the gap between steps
Demand climbs one step every 3 working days by default. Widening that gap reaches the same steady state more slowly, which gives warmup longer to catch up, and it does not reduce the volume eventually sent by a single message. It also tends to improve reply rates rather than harm them, which makes it the cheapest lever on this page in both senses.
Feed prospects in more slowly at the start
Loading the full monthly list on day one guarantees the steepest possible demand curve. Releasing prospects in weekly tranches over the first month flattens it to match the warmup slope. The month sends slightly less in total, and every message it does send comes from a mailbox that was allowed to send it.
Buy mailboxes you will not need at steady state
More warming mailboxes raise the capacity curve, at the price of paying for capacity the programme stops needing once warmup finishes. It works, and it is listed last on purpose: it is the only lever here that costs money, and it is the first one most volume calculators reach for because it is the one their publisher sells.
The order matters. Three of the four levers are free or nearly free, and the one that costs money is the one most volume calculators reach for first, because it is the one their publisher sells.
What the providers publish
How many emails a day can you send per mailbox?
Two different numbers get confused here constantly, and SmartReach.io keeps them apart. There is the limit at which your provider stops you, and there is the rate at which recipients and filters do not start. The first is published, enforced, and between fifty and two hundred and fifty times the second. A sender who reads a provider limit as a target has been told by their own mail provider to do the thing that will get their domain filtered.
| Who | Published limit | What it actually means |
|---|---|---|
| Google Workspace | 2,000 messages a day | 3,000 external recipients a day, of which 2,000 unique external, over a rolling 24 hours rather than a calendar day. Trial accounts are capped at 500. Exceeding it locks sending for up to 24 hours. |
| Microsoft 365 | 10,000 recipients a day | With a message rate limit of 30 messages a minute. Microsoft’s own footnote to that table says Exchange Online "isn’t suited to accommodate bulk-mailing scenarios" and points bulk senders elsewhere, which is a rare thing for a provider to publish about its own product. |
| Microsoft 365, per tenant | Scales with licence count | The Tenant External Recipient Rate Limit caps external recipients across the WHOLE tenant per day, not per mailbox, and depends on how many licences the tenant holds. Trial tenants are capped at 5,000 a day. Stacking mailboxes inside one tenant therefore does not multiply capacity the way dividing by a per-mailbox rate implies. |
| What SmartReach.io recommends | Under 40 a day per mailbox | Between fifty and two hundred and fifty times below what the providers allow. The limits above are the point at which a provider stops you; this is the rate at which recipients and filters do not start. SmartReach.io permits up to 200 a day per connected account and recommends staying under 40, because the number a platform permits and the number a domain survives are not the same number. |
The tenant limit is the one that catches people
Microsoft's Tenant External Recipient Rate Limit caps external recipients across a whole Microsoft 365 tenant per day, scaled to the number of licences it holds, with trial tenants capped at 5,000 a day. Ten mailboxes inside one tenant therefore do not necessarily carry ten mailboxes of volume, which is a result the arithmetic on this page cannot see and your admin console can. It is also the strongest argument for spreading an estate across separate domains and tenants rather than stacking it inside one.
Above 5,000 messages a day to Gmail accounts, Google's sender guidelines apply in full: SPF, DKIM and DMARC on the sending domain, one-click unsubscribe as defined in RFC 8058, and a spam rate under 0.30%. Yahoo's sender best practices name the same 0.3%. The calculator flags a plan approaching that threshold, because unlike almost every other deliverability requirement it is a volume figure, and a volume plan can see it coming.
The category, measured
Why no two cold email calculators give the same answer
SmartReach.io read 9 ranking cold email volume and mailbox calculators in September 2026 and compared the three numbers all of them turn on. On messages a day per mailbox, the single figure every one of these tools exists to apply, their published recommendations run from 3 to 1,000 — a spread of more than three hundred times. On warmup, fourteen days to twelve weeks. On mailboxes per domain, two to five. Run the same target through any two of them and you will be told to buy estates that differ by an order of magnitude. Each page states its own number as though it were settled, and none of them mentions that the others disagree, which is the most useful thing anyone could publish about this category.
| The number | Published range | Why they differ | What SmartReach.io uses, and why |
|---|---|---|---|
| Emails a day per mailbox | 3 to 1,000 | Mostly because the number answers different questions. Some quote a provider limit, which is where sending stops rather than where filtering starts. Some quote a figure for a warmed mailbox on an opted-in list, which is not cold email. At least one splits by provider and treats Microsoft mailboxes as an order of magnitude more fragile than Google ones. And a calculator published by a company that sells mailboxes has an interest in a low number, while one published by a company that sells sending has an interest in a high one. | 40 a day The middle of the range that six of the nine converge on, which is 30 to 50. SmartReach.io permits up to 200 a day per connected account and recommends staying well under it, because the number a platform permits and the number a domain survives are different numbers. |
| Mailboxes per domain | 2 to 5 | This one is a genuine judgement rather than a confusion. Fewer mailboxes on a domain means a smaller blast radius when one is filtered, and more domains to buy, authenticate and maintain. More mailboxes per domain concentrates both the volume and the risk on a single reputation. Nobody in the category shows the figure that would let a reader decide, which is the daily volume each ratio puts on one domain. | 5, and no more than 7 At the top of the published range, and stated as such rather than presented as consensus. At 40 a day that is 200 messages a day resting on one domain's reputation, against roughly 120 at the ratio of three that most of the category uses. The field is editable for exactly that reason: a sender on new domains, or one who cannot afford to lose the whole estate at once, should set it lower. |
| Warmup before full volume | 14 days to 12 weeks | The widest spread of the three, and most of it is one unstated distinction: a brand new mailbox and a pre-warmed one bought from a reseller are not the same object. Guidance written for the first is quoted at people buying the second and the other way round. The rest is that warmup has no specification behind it. SPF, DKIM and DMARC are defined by RFCs anyone can read; warmup is a convention the industry arrived at and continues to argue about. | About 19 working days Roughly 4 weeks, for a new mailbox climbing from 5 a day. Modelled as a curve rather than asserted as a duration, because the duration is not the useful part: what a plan needs to know is what the mailbox may send in week two, which is what the chart on this page draws. |
How to read a per-mailbox number, including this one
Three questions settle almost every disagreement above, and SmartReach.io recommends putting them to any calculator including this one. Which provider is it for, since the published figures for Microsoft mailboxes run far below those for Google ones. Is it for a new mailbox or a pre-warmed one, because a rate that is safe in week eight will get a week-one mailbox filtered. And who is selling what: a figure published by a mailbox reseller and a figure published by a sending platform are both interested numbers, and they are interested in opposite directions. A calculator that does not tell you which of the three applies has not given you an answer, it has given you a number.
The calculators read were BuzzLead, DitLead, HowManyColdEmailsPerDay, IceMail, Litemail, MailTester, Omni Online Strategies, PuzzleInbox and TrulyInbox. Ranges are taken from the published copy of each as it stood on the review date below, and are reported as a spread rather than pinned to individual tools: a figure read once is enough to establish that the disagreement exists and not enough to attribute a contested number to a named company in public.
The bill
What does cold email infrastructure cost?
SmartReach.io prices the estate rather than only counting it, because the mailboxes are the bill and the domains are rounding, which is the opposite of how most teams budget for this. At market rates of about $6 a mailbox a month and $12 a domain a year, the estate for 182 messages a day costs roughly $38 a month, and the one for 1,818 a day about $348. SmartReach.io divides that by the volume it buys, because cost per reply is the figure worth comparing against anything else the same budget could do, and a monthly total on its own is not.
Why the bill is for 120% of the estate
Mailboxes are suspended, rested after a bad patch, replaced and re-warmed, and an estate sized exactly to its own steady state starts skipping sends the first time one is lost. Every working calculator in this category adds a buffer of fifteen to twenty per cent for it, and SmartReach.io budgets at the top of that range and shows both counts so the price of the insurance is visible rather than folded in. The default prices in the fields are market rates for a mailbox and a domain, checked on this page's review date. They are third-party prices rather than SmartReach.io's, they move, and they are editable for that reason.
The arithmetic
How to calculate cold email sending volume
SmartReach.io publishes all six of the formulas behind this cold email volume calculator as text rather than burying them in a script, so any number on this page can be checked by hand. The first two are what every calculator in the category publishes. The last four, including steady-state volume at 40 messages a day per mailbox and what a warming mailbox may send, are the ones that decide whether a plan survives its first month.
| What | Formula | Note |
|---|---|---|
| Monthly sending volume | prospects × steps | Every prospect receives the whole sequence, so a list of 2,000 on a four-step sequence is 8,000 messages, not 2,000. |
| Messages a day | monthly volume ÷ 22 working days | The monthly average. True at steady state, and wrong for the whole ramp that precedes it, which is why it is not what the mailboxes are sized on. |
| Steady-state daily volume | new prospects per day × steps | The number that sizes the estate. Day one sends only the first touch; the second joins it 3 working days later, and steady state is reached once every step is running against a different cohort at once. |
| Mailboxes needed | steady-state daily volume ÷ 40 | Rounded up. 40 a day per mailbox is the SmartReach.io recommendation, not a provider limit: Google Workspace allows 2,000 a day and Exchange Online 10,000 recipients a day. |
| Domains needed | mailboxes ÷ 5 | Rounded up. Reputation attaches to the domain, so this is the number that decides how much of the programme one bad week can take out. |
| What a warming mailbox may send | 5 + 2 × (working days since it started) | Capped at the per-mailbox rate. A new mailbox reaches 40 a day after about 19 working days, so mailboxes bought on the launch date are 4 weeks late. |
Mailboxes per domain is the one figure here that is a judgement rather than a calculation. SmartReach.io recommends 5 and no more than 7, because reputation attaches to the domain: the mailboxes on one domain share a single reputation and are filtered together, so the domain count decides whether a bad week costs part of the programme or all of it. Spreading a campaign evenly across the whole estate once it is built is what inbox rotation does.
The honest answer
What this calculator will not tell you
A volume calculator published by a company that sells sending software has an obvious incentive to make the answer bigger, and the per-mailbox rate is the input that would do it. SmartReach.io sets out what this tool declines to do rather than leaving a reader to discover it.
It does not promise the mail will arrive
Sizing an estate correctly is a precondition for deliverability, not a cause of it. A perfectly sized 5-mailbox domain sending to a bought list will be filtered on schedule. This page answers how much infrastructure a volume needs; whether that volume should be sent to those people is a different question and a more important one.
It does not predict your reply rate
The reply figures are arithmetic on a published benchmark from the SmartReach.io State of Cold Email report, 40M+ emails across 5,000+ campaigns, not a forecast of what your list will do. A team below that benchmark gets fewer replies from the same volume. The figure is there to size the human cost of the sending, not to promise a result.
It will not let you raise the per-mailbox rate quietly
The rate is editable, because a sender with a warmed domain and a genuinely opted-in list is in a different position from a cold one. Raising it returns a finding naming the mailboxes you have decided to do without, because the change does not create capacity, it moves risk onto the domains and out of the budget.
It cannot see your provider tenant
Microsoft caps external recipients across a whole tenant based on licence count, so ten mailboxes in one tenant may not carry ten mailboxes of volume. The calculator sizes mailboxes and domains; whether your provider will let those mailboxes send what they are sized for is a limit only your own admin console can show you.
Once the estate is sized
What the new domains need before they send
A domain with no SPF, DKIM or DMARC published on it sends nothing that arrives, so the next step after sizing an estate is publishing three records on every domain in it. SmartReach.io publishes a free checker and a free generator for each, and the complaint rate calculator is the metric that says afterwards whether the volume this page sized was too much for the domains it sized it across.
All three records, one pass
Email Authentication Checker
Check SPF, DKIM and DMARC on any domain at once. See which of the three are missing, which are broken, and which are published but not actually enforcing anything.
What it looks like
SPF pass · DKIM pass · DMARC p=reject
One record, under the limit
SPF Record Generator
Pick the services that send mail for you and get a single valid SPF record back, with the ten-lookup budget counted live from real DNS as you add each one.
What it looks like
v=spf1 include:_spf.google.com include:amazonses.com ~all
Start monitoring, end enforcing
DMARC Record Generator
Build the record that tells receivers what to do with mail failing SPF and DKIM, and check, live, that the reports it asks for will actually reach you.
What it looks like
v=DMARC1; p=none; rua=mailto:dmarc@example.com
The one rate with a published limit
Spam Complaint Rate Calculator
Work out the share of delivered messages recipients reported as spam, against the 0.30% Google requires and the 0.10% it recommends, and find out whether the campaign was even large enough to express a rate under either.
What it looks like
4 complaints ÷ 2,304 delivered = 0.17%
Provider limits on this page are quoted from Google's published Workspace sending limits, Microsoft's Exchange Online limits and Microsoft's note on tenant outbound limits, and the bulk sender threshold from Google's email sender guidelines. Warmup ramp and follow-up spacing are conventions rather than published standards and are adjustable in the tool. Last reviewed . The calculator is free and ungated, and the figures you enter are not transmitted, stored or logged.
FREQUENTLY ASKED QUESTIONS
Cold email volume questions, answered
Sizing the estate is the easy half. Running it is the other half.
A plan drawn on this page is a set of mailboxes that have to be warmed, rotated through and watched per domain. SmartReach.io is a cold email software with multichannel outreach capabilities via channels like email, LinkedIn, calls and WhatsApp. On its Sales Engagement plans it also works as a sales engagement platform, with no per-seat pricing. It rotates sending across unlimited connected mailboxes, stops a sequence the moment somebody replies, and reports volume per mailbox, per domain and per campaign, so what actually went out is visible against what was planned.