How Many Mailboxes Do You Need?
Size your cold email infrastructure across Google Workspace, Microsoft 365, and Azure. Start from a monthly send volume, or work backwards from the meetings you want to book, and see the mailboxes, domains, and monthly cost it takes.
Start from
About 1,364 emails per day across 22 sending days.
Provider mix
Google70%
Microsoft30%
Azure0%Billing cycle
Warmup
Automated inbox warmup, priced per mailbox.
Deliverability monitoring
DNS and deliverability monitoring, priced per domain.
Effective monthly cost
$465.00 / mo
Projected from your reply and meeting rates. A common benchmark is roughly one meeting per 100 emails sent. Edit the assumptions on the left to match your real numbers.
Volume diversification
Google Workspace
Microsoft 365
How it works
3 quick steps from input to answer. No account, no install.
Back to the tool- 01
Set your volume or goal
Enter a monthly send volume, or switch modes and work backwards from the meetings you want to book each month.
- 02
Split your provider mix
Balance volume across Google Workspace, Microsoft 365, and Azure. Mailboxes and domains are sized per provider.
- 03
Review the cost
See mailboxes, domains, effective monthly cost, and first-year total, with warmup and monitoring add-ons and billing-cycle discounts.
Why this matters
Most cold email campaigns fail because people send too many emails from too few mailboxes. A safe deliverable rate is roughly 15 emails per day per Google Workspace mailbox and about 5 per Microsoft 365 mailbox, with around 3 mailboxes per domain. Getting the math wrong means spam folders, blacklists, and burned domains.
SendboxSet up your infrastructure in minutes
Sendbox gives you unlimited mailboxes on dedicated IPs with automated warmup. Connect, warm up, and start sending.
Unlimited mailboxes
Connect as many mailboxes as you need on every plan
Dedicated IPs
Your own IP addresses. Your sender reputation stays yours.
Automated warmup
Every new mailbox gets warmed up automatically
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Verify your domain email authentication in one click. See which records pass, which fail, and how to fix them.
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Email Verifier
Check if an email address is real before you send. Detects invalid mailboxes, catch-all domains, and SEG-protected addresses.
It depends on your daily send volume. A safe deliverable rate is roughly 15 emails per day per Google Workspace mailbox and about 5 per Microsoft 365 mailbox. To send 1,000 emails a day on Google you need about 67-69 mailboxes across roughly 23 domains. The calculator sizes this automatically from your target volume, or works backwards from the meetings you want to book.
Ready to land in primary?
Get your own isolated Sendbox setup running and start sending inside 15 minutes.
Every plan includes a dedicated IP. Cancel whenever you want.
