Free Mailbox Calculator
Calculate how many domains and mailboxes you need for cold email outreach and for what cost.
Watch How It Works
How To Use This Tool
Cold email deliverability depends on how well you distribute your sending volume across domains and mailboxes. Sending too many emails from a single domain is the fastest way to get flagged as spam — even if your copy is great.
This calculator helps you find the right balance. Enter the total number of emails you want to send per day, or use the campaign settings mode to let the calculator derive it from your list size, emails per lead, and campaign duration.
The sending infrastructure sliders let you tune the ratio of mailboxes per domain and emails per mailbox per day. The risk indicators turn amber or red when you're pushing beyond safe deliverability thresholds — stay in the green zone for best results.