Tools · 1 minute
Cold email inbox calculator
How many domains and mailboxes you need to send your target volume safely, what it costs and when you can start.
How the calculation works
Mailboxes needed = daily cold emails ÷ emails per mailbox, rounded up. Domains = mailboxes ÷ mailboxes per domain, rounded up, plus about one spare for every four domains. Cost = domains × yearly price ÷ 12, plus mailboxes × monthly price. Full volume starts after a five-week warm-up.
Warm-up plan per new mailbox
| When | Warm-up emails per day | Cold emails per day |
|---|---|---|
| Week 1 | 5 to 10 | None |
| Week 2 | 10 to 20 | None |
| Week 3 | 20 to 30 | Up to 10 |
| Week 4 | 30 to 40 | 10 to 20 |
| Week 5 onwards | Keep it on | 20 to 30, never above about 50 |
Weekly health check: spam complaints below 0.1% (act above 0.3%), bounces below 2% (act above 3%), warm-up inbox placement above 90%. Google’s sender guidelines set the 0.1% and 0.3% spam thresholds.
Questions people ask
How many cold emails can one mailbox send per day?
Most practitioners keep cold sends to roughly 15 to 35 per mailbox per day after warm-up. This calculator uses 30 by default. Lower it if you see bounces or spam complaints rising.
How many mailboxes should I put on one domain?
Two or three. More mailboxes on one domain concentrates risk: if the domain gets a bad reputation, every mailbox on it suffers.
Why not send cold email from my main domain?
If cold email from your main domain lands in spam, your customer emails, invoices and team email can follow. Separate look-alike domains protect it.
How long does warm-up take?
Plan for three to five weeks before real cold volume, and keep warm-up running afterwards. New mailboxes that send cold email straight away tend to land in spam.