Cold Email Mailbox Calculator
Enter your target daily outreach volume and instantly see how many mailboxes, domains and dollars it takes — side-by-side across Google, Microsoft, Azure and IMAP/SMTP.
How many mailboxes do you need?
Size mailboxes, domains and monthly cost for your outreach — and see what you save vs typical infra resellers.
How many emails each contact receives in your sequence
Apples-to-apples vs Inframail, Zapmail, Mailreef · Google infra ($3.50 / mailbox).
Each mailbox runs warmup at a 1:1 ratio (parallel by default). Plan your launch 14 days ahead.
Based on 22 weekday sending days/month and provider daily limits. Warmup model: parallel. Estimate only.
How the calculator works
We start from your daily outreach volume — the number of cold emails you want to send per day. Each provider has a safe daily send cap per mailbox (15/day for Google & Microsoft, 5/day for Azure, 25/day for IMAP/SMTP) and a maximum number of mailboxes per domain.
The calculator divides your daily volume by the per-mailbox safe limit to compute mailboxes needed, then divides mailboxes by the per-domain cap to compute domains needed. Cost is then derived from each provider's pricing model — per-mailbox for Google/Microsoft, flat per-domain for Azure and IMAP/SMTP.
Warmup mode: by default warmup is treated as parallel (in addition to outreach). Flip to Strict if your platform counts warmup against the daily cap — the calculator will double mailboxes accordingly.
Use this to plan budget: spread risk across providers (e.g. Google for primary + Azure for volume), or pick a single provider based on cost-per-send at your scale.