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).
Based on 22 weekday sending days/month and provider daily limits. 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.