Mailboxes = daily cold emails ÷ cold emails per mailbox, rounded up. Domains = mailboxes ÷ mailboxes per domain. Plan on 10 to 20 cold emails per mailbox per day (15 is the default) and 5 mailboxes per domain. For 1,000 cold emails a day that is 67 mailboxes on 14 domains, which costs $86 a month on Winnr Startup, or $126.20 with built-in warming.
Cold email calculator
Change any input and the results update. Everything runs in your browser.
Work it out from your prospect list
10,000 × 3 ÷ 22 days = 1,364 cold emails per day
- Startup plan
- $69
- Extra mailboxes
- $17
- Warming (67 × $0.60)
- $40.20
- Monthly cost
- $126.20
- Cost per mailbox
- $1.88
- Cost per 1,000 cold emails
- $5.74
- Domains, one-time (estimate)
- about $182
22,000 cold emails a month. Total capacity about 3,350 emails a day including warming.
Mailbox cost compared
For the 67 mailboxes above. Mailbox licences only: domains are extra everywhere.
| Option | Per month | Per mailbox | Per 1,000 cold emails |
|---|---|---|---|
| Winnr (your setup) | $126.20 | $1.88 | $5.74 |
| Winnr, without warming | $86 | $1.28 | $3.91 |
| Google Workspace Business Starter, annual ($7/user) | $469 | $7 | $21.32 |
| Google Workspace Business Starter, flexible ($8.40/user) | $562.80 | $8.40 | $25.58 |
| Microsoft 365 Business Basic, annual ($7/user) | $469 | $7 | $21.32 |
Google and Microsoft prices are US list prices as of October 2026 (Google Workspace pricing, Microsoft's July 2026 price update). They include office apps and do not include warming. Winnr prices are from the pricing page. The domain figure is an estimate at about $13 per .com; real prices are per extension and shown at checkout.
How the calculator works
Every number comes from a few simple formulas. Results are rounded up, because you can't buy part of a mailbox or a domain.
Mailboxes = daily cold emails ÷ cold emails per mailbox per day
Domains = mailboxes ÷ mailboxes per domain
Plan = the cheaper of Startup ($69 + $1 per mailbox above 50) and Enterprise ($189 + $1 per mailbox above 200)
Monthly cost = plan + mailboxes × $0.60 if warming is on
Cost per 1,000 cold emails = monthly cost ÷ (daily cold emails × sending days) × 1,000
Domains, one-time = domains × about $13 (minus 5 free on Enterprise, or $0 if you bring your own)
Worked example: a list of 10,000 prospects, 3 emails each (one first touch and two follow-ups), spread over 22 weekdays. That is 30,000 emails, or 1,364 a day. At 15 per mailbox you need 91 mailboxes on 19 domains. Startup covers 50 of them and the other 41 cost $1 each, so the plan costs $110 a month, or $164.60 with warming on all 91.
Cold emails per mailbox: 10, 15 or 20
A Winnr mailbox sends about 50 emails a day in total, and that figure includes warming traffic. Cold email to prospects should be a fraction of it: 10 to 20 per mailbox per day, with 15 as the default. The plan figures on the pricing page (about 2,500 emails a day on Startup, 10,000 on Enterprise) are totals including warming, not cold email capacity.
| Cold per mailbox per day | Mailboxes for 1,000 a day | Domains (5 per domain) | Winnr per month, with warming | When to use it |
|---|---|---|---|---|
| 10 | 100 | 20 | $179 | New domains, a domain recovering its reputation, or a market where one spam complaint is costly |
| 15 (default) | 67 | 14 | $126.20 | Most teams |
| 20 | 50 | 10 | $99 | Fully warmed mailboxes on aged domains with a clean sending history |
Above 20 per mailbox the calculator shows a warning. If you need more volume, add mailboxes rather than raising the per-mailbox number: mailboxes are $1 each beyond your plan, so the extra cost is small.
Mailboxes per domain
Five mailboxes per domain is the common default, and it is what the calculator starts with. Putting fewer on each domain spreads risk: if one domain picks up a reputation problem, fewer mailboxes are affected. The trade-off is more domains to buy. Domain slots on Winnr are free to raise in Settings, so the slot count is never the constraint. For more on picking and spreading domains, see cold email domains.
Worked examples
At 15 cold emails per mailbox, 5 mailboxes per domain, warming on and 22 sending days a month:
| Cold emails per day | Mailboxes | Domains | Plan | Per month, with warming | Domains, one-time (estimate) |
|---|---|---|---|---|---|
| 250 | 17 | 4 | Startup | $79.20 | about $52 |
| 500 | 34 | 7 | Startup | $89.40 | about $91 |
| 1,000 | 67 | 14 | Startup + 17 extra | $126.20 | about $182 |
| 2,000 | 134 | 27 | Startup + 84 extra | $233.40 | about $351 |
| 3,000 | 200 | 40 | Enterprise | $309 | about $455 (5 free) |
| 5,000 | 334 | 67 | Enterprise + 134 extra | $523.40 | about $806 (5 free) |
Startup includes 50 mailboxes, so small targets still cost $69 a month for the plan. Warming is charged only on the mailboxes you warm.
Startup or Enterprise
Startup is $69 a month with 50 mailboxes. Enterprise is $189 a month with 200. Extra mailboxes are $1 each per month on either plan. That makes the crossover easy to find: 50 mailboxes plus 120 extras on Startup costs $189, the same as Enterprise. So:
- Up to 169 mailboxes: Startup plus extras is cheaper.
- 170 mailboxes: both cost $189. The calculator recommends Enterprise, because it includes 30 more mailboxes for the same price.
- Above 170: Enterprise is cheaper, and it adds 5 free domain purchases, optional dedicated IPs ($20 per IP per month), white-glove domain setup, and phone, WhatsApp and Slack support.
Both plans are billed monthly with no annual contract. If your mailboxes aren't reaching 90% deliverability, ask and Winnr refunds your most recent month. Full details are on the pricing page.
Winnr vs Google Workspace vs Microsoft 365
With Google Workspace or Microsoft 365, each sending mailbox is a paid user. As of October 2026, Google Workspace Business Starter lists at $7 per user per month on an annual plan and $8.40 on the flexible plan, and Microsoft 365 Business Basic lists at $7 per user per month with an annual commitment (it rose from $6 on July 1, 2026). At 100 mailboxes:
| 100 mailboxes | Per month | Per mailbox |
|---|---|---|
| Winnr Startup + 50 extra | $119 | $1.19 |
| Winnr Startup + 50 extra, with warming | $179 | $1.79 |
| Google Workspace Business Starter, annual | $700 | $7 |
| Google Workspace Business Starter, flexible | $840 | $8.40 |
| Microsoft 365 Business Basic, annual | $700 | $7 |
The comparison is about mailbox cost, not features. Google Workspace and Microsoft 365 include office apps, storage and video calls, and some teams want those inboxes for other reasons. Winnr mailboxes are SMTP/IMAP accounts built for sending, with warming built in and DKIM, SPF and DMARC set up automatically. For the full trade-off, read the Google Workspace alternative for cold email or SMTP for cold email.
Warming time and spare mailboxes
- Warming time: a new mailbox needs 2 to 4 weeks of warming before it carries full cold volume. Winnr's built-in warming is $0.60 per mailbox per month, so start it as soon as the mailboxes exist.
- Spare mailboxes: add 10 to 15% more than the calculator shows, so you can rest a mailbox or replace a domain without pausing a campaign.
- Need volume this week: pre-warmed mailboxes are already warmed and ready to send the same day, at $3 per address per month with no minimum term.
Before you send, check each domain's records with the domain health checker, and plan the ramp with the warmup schedule generator.
Frequently asked questions
How many mailboxes do I need for cold email?
Divide your daily cold email target by the number of cold emails each mailbox sends per day, then round up. At the recommended 15 per mailbox, 1,000 cold emails a day needs 67 mailboxes. At 10 per mailbox it needs 100, and at 20 it needs 50.
How many cold emails should one mailbox send per day?
Plan on 10 to 20 cold emails per mailbox per day, with 15 as the default. A Winnr mailbox sends about 50 emails a day in total, and that total includes warming traffic, so cold email is only part of it. To send more, add mailboxes instead of raising the per-mailbox number.
How many mailboxes should I put on each domain?
Five is the usual default and the calculator starts there. Fewer mailboxes per domain spreads risk, because one domain with a reputation problem affects fewer mailboxes, but you buy more domains. The calculator accepts 1 to 10.
How many mailboxes do I need for 10,000 cold emails a month?
Sending on weekdays (22 days a month), 10,000 cold emails is about 455 a day. That needs 31 mailboxes at 15 per mailbox, 46 at 10, or 23 at 20. At 5 mailboxes per domain, 31 mailboxes fit on 7 domains, and the Winnr Startup plan covers it at $69 a month ($87.60 with warming).
Which Winnr plan do I need?
Startup is $69 a month with 50 mailboxes included, and Enterprise is $189 a month with 200 included. Extra mailboxes are $1 each per month on either plan. Startup plus extras is cheaper up to 169 mailboxes, both cost $189 at 170, and above that Enterprise is cheaper. The calculator picks the cheaper plan for you, and you can override it.
Is warming included in the price?
Warming is built into Winnr as an add-on at $0.60 per mailbox per month. The calculator includes it by default because new mailboxes should warm for 2 to 4 weeks before they carry cold volume. Untick it to see the cost without warming.
How much do the domains cost?
Domains are a one-time purchase priced per extension at checkout. A .com is about $13, so the calculator uses $13 per domain as an estimate. Enterprise includes 5 free domain purchases, and connecting domains you already own is free.
How does Winnr compare on cost with Google Workspace or Microsoft 365?
On Google Workspace or Microsoft 365, every sending mailbox is a paid user. As of October 2026, Google Workspace Business Starter lists at $7 per user per month on an annual plan ($8.40 flexible), and Microsoft 365 Business Basic lists at $7 per user per month with an annual commitment. For 100 mailboxes that is $700 a month on either, against $119 on Winnr Startup ($179 with warming). Google and Microsoft also include office apps, which Winnr does not. Winnr mailboxes are SMTP/IMAP accounts built for sending.
What does cost per 1,000 cold emails mean?
It is your monthly Winnr cost divided by the cold emails you send in a month, times 1,000. Monthly volume is your daily target times your sending days, which defaults to 22 weekdays. Warming emails are not counted, because they do not reach prospects.
Should I add spare mailboxes?
Yes. Add 10 to 15% more mailboxes than the calculator shows, so you can rest a mailbox or replace a domain without pausing campaigns. If you need sending capacity right away, pre-warmed mailboxes are ready to send the same day at $3 per address per month.