Free tool
Cold email capacity calculator
Divide your monthly volume by 550: that is how many cold emails one mailbox sends in a month at 25 a working day. Add about 20% spare mailboxes, and put up to 5 mailboxes on each domain. 50,000 emails a month needs 91 sending mailboxes, 19 spares and 22 domains.
Plan two weeks of warm-up before the first cold email and a week of ramp after it. The calculator below does the math for any volume and prices it.
Timeline
- 1. Set up · Day 0Buy 22 domains, set SPF, DKIM and DMARC, create 110 mailboxes.
- 2. Warm up · Days 1 to 14Warm-up only, no cold email. Keep warm-up running afterwards at a low volume.
- 3. Ramp · Week 3Start at about 10 cold emails per mailbox a day and raise it to 25 over the week. Watch bounces and replies per domain.
- 4. Full volume · Week 491 mailboxes at 25 a day, about 2,273 emails a working day. 19 spare mailboxes stay warm to replace any that slip.
How it works
How the numbers are set
- 25 new cold emails per mailbox per working day, 22 working days a month. Follow-ups count toward the 25.
- Up to 5 mailboxes per domain. Fewer per domain (2 or 3) spreads risk further at the cost of more domains.
- 20% spare mailboxes by default: they warm up alongside the others and replace any mailbox or domain that starts landing in spam.
- Mailboxes at $2.50 a month each with warm-up and sending included (Outreach2day, minimum 12). Domains at $13 a year for .com or $5 for .info. Change the prices to compare with your current setup.
Background
Why 25 a day per mailbox
Mailbox providers judge each sender by its volume history and by how recipients react. A mailbox that sends a steady, modest volume to people who sometimes reply looks like a person. Hundreds a day from one new mailbox does not.
Scaling cold email means adding mailboxes and domains, not raising the per-mailbox number. If replies drop or bounces rise on one domain, you rest that domain and the rest keep sending.
FAQ
Questions
How many cold emails can one mailbox send per day?
We plan 25 new cold emails per mailbox per working day, including follow-ups. Some teams go to 30 to 50 on older, well-warmed mailboxes; it raises the risk for that mailbox and its domain.
How many mailboxes should I put on one domain?
Up to 5. Three or fewer spreads the risk further: if a domain's reputation drops, fewer mailboxes go with it.
How long does warm-up take before cold emails?
At least two weeks for new mailboxes, then a week of ramp from about 10 to 25 cold emails a day. Keep warm-up running at a low volume while you send.
Should I send cold email from my main company domain?
No. Use separate domains that redirect to your site, so a drop in cold email reputation never touches the domain your team and customers use.
In your AI assistant
Run the same checks in Claude or ChatGPT
Free SKILL.md files with the rules behind this tool. Install them in Claude or Claude Code, or paste them into ChatGPT, Gemini, Grok or Cursor.
Mailboxes, warm-up and sending in one place
$2.50 a mailbox a month. DNS records are set for you, and every mailbox shows its warm-up numbers from day one.