How Many Mailboxes Do I Need to Send N Cold Emails a Day?

The formula

1. Mailboxes = cold emails per day ÷ 25

2. Domains = mailboxes ÷ 5

3. Round both up, and add spare domains.

The 25 is the per-mailbox ceiling for cold email, not counting warm-up. The 5 is mailboxes per domain. See cold emails per mailbox per day and mailboxes per domain.

Worked examples

These count working days. If you send only on weekdays, divide your monthly target by the number of sending days, not by 30.

Start from the result, not the volume

Volume is a means. A better starting point:

1. How many meetings or opportunities do you need a month?

2. How many emails does one meeting take for you today? Use your own numbers from past campaigns.

3. Multiply, then divide by your sending days. That is your daily volume.

4. Apply the formula above.

If you have no history yet, start small, measure for a few weeks, then size up. Google's sender guidelines give the same advice for volume in general: "Start with a low sending volume to engaged users, and slowly increase the volume over time."

Plan for spare capacity

• Spare domains. Domains wear out, and a replacement needs three weeks of warm-up. Keep a few warmed spare domains so a burned one doesn't cut your volume.

• Headroom per mailbox. Running a little below 25 per mailbox gives you room to absorb a paused domain without pushing the others over the limit.

• Separate campaigns for Google and Outlook recipients if your list is split, so you can measure each.

Timeline

Scale up by adding new batches of mailboxes on this same schedule, not by raising per-mailbox volume.

Don't forget the sending side

More mailboxes means more to manage: connections to your sending tool, reply handling and monitoring per mailbox and per domain. Plan how replies from all mailboxes reach one place before you add the tenth domain.

What we recommend at Outreach2day

Up to 25 cold emails per mailbox a day, not counting warm-up, on up to 5 mailboxes per domain. For 1,000 emails a day that is 40 mailboxes ($100 a month) on 8 domains ($104 a year as .com). See pricing, and the send 100,000 cold emails a month guide for larger setups.