Your funnel (your own numbers work best)
Defaults are starting assumptions, not benchmarks: change them to your own numbers. Inbox price default = $3.00 per Google Workspace or Microsoft 365 mailbox on monthly billing ($2.50 a month on annual billing), as published by InboxKit on 2026-10-09; warm-up add-on not included. The domain price is an estimate: check your registrar. Warm new inboxes for 2-3 weeks before full volume.
Get your sending domains and inboxes set up for you
B2BX Infra sets up Google Workspace and Microsoft 365 inboxes on new domains with SPF, DKIM and DMARC already in place, ready to warm up.
How the maths works
Emails per month = new prospects x emails per prospect Inboxes needed = emails per month / (emails per inbox per day x sending days) Domains needed = inboxes / inboxes per domain Monthly cost = inboxes x inbox price + domains x (domain price / 12) + tools and data Meetings per month = new prospects x reply rate x positive share x booking rate Cost per meeting = monthly cost / meetings per month
Choosing sensible inputs
- Emails per inbox per day: keep it low. Sending a modest number of emails from more inboxes protects your reputation far better than pushing a few inboxes hard.
- Inboxes per domain: spreading inboxes across several domains means one problem domain does not take your whole program down.
- Warm-up: new inboxes need two to three weeks of gradual warm-up before full volume, so plan the first month at reduced capacity.
- Funnel rates: use your own numbers from past campaigns. If you have none yet, run the calculator with a low and a high case to see the range.
The cost here is infrastructure only: it leaves out the time to research lists, write copy and handle replies. For the full picture of in-house versus agency costs, read what outbound lead generation costs in 2026. Then check every new domain with the email DNS checker.
Frequently asked questions
How many emails can one inbox send a day for cold email?
There is no official number. Most outbound teams keep cold volume per inbox low and add inboxes to grow, because high volume from one inbox is what damages its reputation. Use a conservative figure in the calculator and raise it only if your deliverability stays healthy.
Why use separate domains for cold email?
So that any deliverability problem stays on a sending domain and never reaches the domain your customers, invoices and team email depend on.
How long before new inboxes can send at full volume?
Plan two to three weeks of gradual warm-up for new inboxes and domains before running full cold volume.
Is the cost per meeting here my real cost per meeting?
It is the infrastructure part only. Add the cost of data, copywriting, reply handling and management time for the full cost per meeting.