How Many Mailboxes Do You Need for Cold Email?

Start from your daily sending limit per mailbox

Most cold-email teams cap each mailbox at roughly 20–30 sends per day once it's warmed up, to protect deliverability. New mailboxes typically start lower, around 5–10 a day, and ramp up over 2–4 weeks of warmup before reaching that ceiling.

The basic formula

Mailboxes needed = target daily emails ÷ sends per mailbox per day. For example, a campaign that wants to send 500 emails a day, at 25 sends per mailbox, needs about 20 mailboxes.

How many domains?

Spread mailboxes across domains rather than one, so a single domain's reputation doesn't control your whole campaign. A common pattern is 2–3 mailboxes per domain on Google Workspace or Outlook. On InboxKit, an Azure domain works differently: one domain supports up to 100 mailboxes, so far fewer domains are needed at volume.

Cost at each volume

At $3.00/mailbox on Google or Outlook, 20 mailboxes cost $60.00/month before any discount. With GET50, that drops to $51.00–$48.00 depending on provider. On Azure, the equivalent capacity (one domain, up to 100 mailboxes) costs $15.00 with the coupon, regardless of how many of those 100 you actually use. Try the exact numbers in our savings calculator.

Add warmup ($3.00/mailbox/month) for new mailboxes, and budget 2–4 weeks of ramp-up before they reach full sending volume.