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Mailbox calculator

Estimate how many mailboxes and sending domains you need to deliver a target daily volume safely — without crossing per-mailbox or per-domain caps.

Inputs

Total emails / day Emails / mailbox / day Warmy / WUI default: 30–80. We recommend 40 for new accounts, 80 once warm. Mailboxes / domain Provider-dependent. Google Workspace: up to 30; cold-email best practice: 8–10.

Results

Mailboxes required

Domains required

Based on 1,000 emails / day, 40 / mailbox, 8 / domain.

How it works

We round up at every step (ceiling division). 1 email per day still needs 1 full mailbox; 17 mailboxes at 8 / domain still need 3 domains. The math is intentionally conservative — better to over-provision than to push a mailbox past its cap and trip ESP filters.

For warmup-friendly volumes during the first 30 days, target 40 sends / mailbox / day and grow from there. See our deliverability guide (coming soon) for the full ramp curve.