Plan how many mailboxes, domains, and tenants your outreach needs. Start from your monthly send volume, or work backward from a meeting goal — then split the load across Google Workspace, Microsoft 365, Azure, or your own provider.
Every starting value is an editable example assumption — change anything to match your plan. Results update as you type.
You need about 42 mailboxes
35 active + 7 spare across 14 domain(s)/tenant(s), for roughly 30,000 emails per month.
| Provider | Share | Mailboxes | Domains/Tenants | Cost / month |
|---|---|---|---|---|
| Google Workspacebilled annual ($1,944.00/cycle) | 70% | 30 | 10 domain(s) .com | $162.00 |
| Microsoft 365 | 20% | 8 | 3 domain(s) .com | $48.00 |
| Microsoft Azure | 10% | 4 | 1 tenant(s) | $12.00 |
| Custom provider | 0% | 0 | 0 domain(s) .com | $0.00 |
monthly volume ÷ sending days per month⌈ daily volume ÷ daily sends per mailbox ⌉active mailboxes + ⌈ active mailboxes × reserve % ⌉largest-remainder split of total mailboxes by provider share %⌈ provider mailboxes ÷ mailboxes per domain or tenant ⌉Σ mailboxes × cost per mailbox × (1 − billing adjustment %)12 × (monthly mailbox cost + add-ons) + annual domain/tenant costEstimates use editable example assumptions (config v2026-09-16) — not official provider limits, not provider or SalesBlink prices, and not a deliverability guarantee.
This calculator runs entirely in your browser. Your volumes, rates, and costs are never sent to SalesBlink or anywhere else, and nothing is stored.
Enter the number of emails you want to send each month, or switch modes and enter a monthly meeting goal with your expected positive-reply and reply-to-meeting rates.
Choose sending days per month, planned daily sends per mailbox, and a reserve percentage for spare mailboxes. Every starting value is an editable example, not a rule.
Split mailboxes between Google Workspace, Microsoft 365, Azure, and an optional custom provider with a preset or your own percentages. Shares must add up to 100%.
See active, spare, and total mailboxes, domains or tenants per provider, effective monthly cost, annual domain cost, and a first-year total — with the formulas shown so you can audit every number.
Verify email addresses before sending so your new mailboxes stay off bounce lists.
Open toolScan your email copy for spam-triggering words before you ramp up sending volume.
Open toolGenerate likely email address permutations for the prospects you plan to contact.
Open toolThere is no single safe number — each provider publishes its own technical sending limits, and cold outreach best practice is to stay far below them. This calculator starts with an editable example assumption of 40 planned sends per mailbox per day and compares it against per-provider example ceilings, but you should set values that match your own warmup stage and provider terms.
Reserve mailboxes give you rotation capacity while others warm up, recover from a reputation dip, or get replaced. A 10–25% reserve is a common planning cushion; the default here is an editable 20% example.
Enter how many meetings you want per month, your expected positive reply rate, and how often a positive reply becomes a booked meeting. The calculator divides the goal by both rates to estimate the monthly send volume required, then sizes mailboxes from that volume with ceiling arithmetic.
Google Workspace, Microsoft 365, and custom providers are sized by mailboxes per domain, so the calculator divides allocated mailboxes by your mailboxes-per-domain setting. Azure is sized by mailboxes per tenant instead. Both unit types feed the annual domain/tenant budget line.
No. All costs are editable example estimates for budgeting only — they are not official Google, Microsoft, or Azure pricing, and they are not SalesBlink prices. Check each provider’s current pricing and enter your own numbers before making purchasing decisions.
No. Mailbox count is an infrastructure planning estimate, not a deliverability guarantee. Inbox placement also depends on warmup, list quality, content, authentication (SPF, DKIM, DMARC), and sender reputation.
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