Cold emailmailbox calculator.
Work out how many mailboxes and domains you need to reach your monthly sending goal at a safe pace, and what the mailboxes cost.
How it works
- Set your goalNew people a month
- See what you needMailboxes, domains, emails a day
- Plan the costAt mailzy's live price
Free, no sign-up. Runs in your browser. Nothing you type is sent anywhere.
The tool
Your sending goal
Everyone you email for the first time; follow-ups don't count.
The first email plus follow-ups. 3 to 5 is normal.
30 keeps each mailbox safe. Higher burns them faster.
Counts 20 sending days a month (Monday to Friday) and 3 mailboxes per domain, the safe number.
What you need
Before you send
- Never send cold email from your main domain: use separate domains that point to it.
- Warm every new mailbox for two weeks before it sends a campaign.
- Keep bounces under 2%: verify every list first.
Why volume is spread out.
What the result means, and how to fix what it finds.
Each mailbox sends a little
Inbox providers watch how much each mailbox sends. A mailbox that sends a few dozen emails a day looks like a person; one that sends hundreds looks like a spammer. So cold email at volume is spread across many mailboxes, each sending around 30 a day. The calculator uses the same numbers mailzy recommends.
Count every email, not every person
Each person usually gets three to five emails: the first and its follow-ups. Reaching 2,500 people with four emails each is 10,000 emails a month. Spread across about 20 sending days, that's 500 a day, or about 17 mailboxes at 30 a day.
Three mailboxes per domain
Put no more than three mailboxes on one domain. If a domain's reputation suffers, only those mailboxes are affected, and inbox providers see a normal-looking number of senders per domain. Never send cold email from your company's main domain: use separate domains that point to your website.
Allow for warm-up
New mailboxes need about two weeks of warm-up before they send campaigns, and campaign volume should build up over a further week. Plan your first campaign three weeks after the mailboxes are ready, or start with fewer people and grow.
Growing over time
Plan mailbox numbers a month ahead. New mailboxes take about three weeks before they send at full volume, so if you expect to reach more people next month, add the mailboxes now. Keep a few spare: a mailbox can be paused for a while if its health drops, and the others should be able to take its share without going over their safe limit. When you add domains, spread campaigns across them, so no single domain carries most of your sending. And review the numbers each month against your reply rates, not just against how many emails you'd like to send.
In mailzy
Google Workspace mailboxes, warmed for you.
Order the number you need. We set up the domains' records, create the mailboxes within 48 hours and warm them up.
Questions before you start.
Ask us on the chat if yours isn't here. A real person answers.
How many emails can one mailbox send a day?
Around 30 cold emails a day is the safe number per mailbox. Google allows far more, but cold email at that volume burns a mailbox's reputation.
Why not send from my main domain?
If its reputation suffers, your normal business email suffers too. Use separate domains for cold email.
What do the mailboxes cost?
Google Workspace mailboxes from mailzy are $4 each a month, with warm-up included.
How many inboxes per domain should I use for cold email?
We recommend 3 per domain, at about 30 campaign emails a day each. If a domain has trouble, only those three mailboxes are affected.
Everything for cold email, in one place.
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