Cold email volume calculator: how many inboxes and domains do you need?
To plan cold email volume, divide the emails you want to send each day by what one inbox should send, and round up: that is your inbox count. Divide inboxes by how many you put on each domain to get sending domains. The calculator does both, adds warm-up time and monthly volume, and flags anything over Google's published limits.
Assumption, adjust it. Instantly's help centre suggests 30 to 50; no mailbox provider publishes a safe cold number.
Assumption, adjust it. Instantly advises at most 3 to 5 accounts per domain; fewer spreads the risk.
Assumption, adjust it. Two to four weeks of rising volume is a common target for a new inbox.
Used to estimate how many new addresses you need each month.
- Inboxes needed
- 17
- Sending domains
- 6
- Full volume from
- 3 wk
- Emails a month
- 10,833
17 inboxes at 30 a day each cover 510 sends, spread over 6 domains with up to 3 inboxes each. With a 3-step sequence that is about 3,611 new prospects a month. Set the inboxes up now and plan on 3 weeks of rising volume before the full 500 a day.
Next step
That plan needs about 3,611 new addresses a month. Every bounce counts against those 17 inboxes.
Hard bounces hurt the reputation of the inboxes and domains you just planned, and a list you didn't collect yourself always has dead addresses in it. Verify each batch before it goes into a campaign: $29.99 a month, unlimited.
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Sample result
Sending 500 cold emails a day at 30 per inbox takes 17 inboxes across 6 domains.
- Inboxes needed
- 17
- Sending domains
- 6
- Emails a month
- 10,833
What this means for you
Set these up and warm them before launch, so no single inbox sends more than 30 a day.
- Inboxes and domains for a daily target
- Warns above 2,000 a day per mailbox
- Flags the 5,000-a-day bulk sender line
- New prospects needed each month
- Inboxes
- Domains
- Volume
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
How do I calculate how many inboxes I need for cold email?
- Enter how many cold emails you want to send per day once everything is warmed up.
- Set sends per inbox per day and inboxes per domain to your own numbers. The defaults are assumptions, not rules.
- Set your warm-up period, sending days per week and how many emails each prospect gets in the sequence.
- Read the inboxes, domains, date you reach full volume and how many new addresses you need each month. Any line crossing a published provider limit is flagged.
Example
- You enter
- 500 cold emails a day, 30 sends per inbox, 3 inboxes per domain, 5 sending days a week and a 3-step sequence.
- You get
- 17 inboxes across 6 domains, 90 sends per domain a day, 10,833 emails a month and 3,611 new prospects needed each month, with no published limit crossed.
- Limits
- No limit; runs in your browser.
How do you calculate how many inboxes you need for cold email?
Inboxes = daily sends ÷ sends per inbox, rounded up, and domains = inboxes ÷ inboxes per domain, rounded up. 500 a day at 30 per inbox is 17 inboxes; at 3 per domain that is 6 domains. Monthly volume uses your sending days and the average 4.33 weeks in a month, and new prospects divide that by the number of steps in your sequence.
No mailbox provider publishes a safe number of cold emails per inbox, because Google's sender guidelines say not to email people who didn't sign up. The default of 30 is a rule of thumb from cold email platforms' own advice: Instantly's cold email strategy article suggests 30 to 50 a day per account, at most 3 to 5 accounts per domain, and at least two weeks of warm-up. Treat those as a starting point and let your own bounce and reply numbers move them.
How many inboxes per domain for cold email?
No mailbox provider sets a number; the calculator defaults to 3, at the low end of the 3 to 5 that Instantly suggests. Fewer inboxes per domain means each domain carries less volume, so a reputation problem on one domain hits a smaller share of your sending.
Gmail's bulk sender line is the reason the per-domain number matters. Google's bulk sender FAQ counts every message from the same primary domain, subdomains included, and a domain that sends close to 5,000 a day to personal Gmail accounts is classified as a bulk sender permanently. Spreading volume across more inboxes on one domain doesn't avoid it; spreading it across domains does. The full rules are in Gmail and Yahoo bulk sender requirements.
What are the real sending limits per inbox?
Google Workspace allows 2,000 messages per user per day and Microsoft 365 allows 10,000 recipients per mailbox per day; both are abuse ceilings, far above any sensible cold volume. Go over the Workspace limit (Gmail sending limits in Google Workspace) and the account is blocked from sending for up to 24 hours. The Microsoft figure is in Exchange Online limits. Every published limit, by account type, is in our sending limits calculator.
How long does warm-up add before you reach full volume?
The warm-up weeks you enter are added to today's date: the result is when the inboxes can carry the full load, not when you can start. A new inbox on a new domain has no sending history, and Google warns in its guidelines that suddenly doubling volume "could result in rate limiting or reputation drops". The usual plan is a few weeks of rising volume before campaigns. Our warm-up calculator builds the week-by-week ramp, and the warm-up schedule guide explains it.
The calculator assumes all inboxes start together. If you are adding capacity to a working setup, only the new inboxes need warming, and you can keep sending from the old ones meanwhile.
Will more inboxes fix a high bounce rate?
No. Adding inboxes spreads volume, but every hard bounce still lands on one of them. Cold email platforms pause campaigns on bounce rate (Instantly's default is 5%, lemlist alerts at 10%), and mailbox providers judge each sending domain on what it sends. A list with 8% dead addresses burns through new inboxes as fast as you can set them up. See bounce rate limits by platform for the published lines, or use our bounce rate calculator on your last campaign.
Can I work this out in a spreadsheet instead?
Yes, the maths is a few formulas. With your daily target in A2, sends per inbox in B2, inboxes per domain in C2, sending days per week in D2 and sequence steps in E2:
| Spreadsheet formula | This calculator | |
|---|---|---|
| Inboxes | =ROUNDUP(A2/B2,0) | Same result |
| Sending domains | =ROUNDUP(ROUNDUP(A2/B2,0)/C2,0) | Same result |
| Emails per month | =ROUND(A2*D2*52/12,0) | Same result |
| New prospects per month | =ROUND(A2*D2*52/12/E2,0) | Same result |
| Date at full volume | =TODAY()+F2*7 with warm-up weeks in F2 | Shown automatically |
| Google limit warnings | Look them up yourself | Flagged against published limits |
The formulas are the calculator's own: it rounds inboxes and domains up, and uses 52 ÷ 12 weeks per month.
Who uses this tool, and for what?
- Cold emailers
- Size a new setup before buying anything: how many inboxes and domains a daily target needs, and the date it can actually run at full volume after warm-up.
- Agencies
- Quote infrastructure per client. A client asking for 1,000 emails a day needs a specific number of inboxes and domains, and the warm-up date tells them when campaigns can reach full speed.
- Sales ops
- Turn a pipeline target into list demand: the new prospects per month figure is how many verified contacts the data team has to supply. Pair it with the verification cost calculator to budget for checking them.
- SaaS teams
- Founders starting outbound can check whether a small test, say 100 a day, fits on one domain and how long the ramp takes before a launch date.
What can’t this tool tell you?
- The per-inbox and per-domain defaults are rules of thumb from cold email platforms, not provider limits. Your own bounce, complaint and reply numbers should set them.
- It assumes every inbox starts warming on the same day and finishes after the weeks you enter. It doesn't model a ramp that slows down because of deferrals or complaints.
- New prospects per month assumes every prospect receives every step. Replies, unsubscribes and bounces stop sequences early, so you need slightly more contacts than shown.
- Monthly volume uses an average month of 4.33 weeks, so a specific month with more or fewer sending days will differ.
- It says nothing about whether mail reaches the inbox. That depends on authentication, list quality and content.
Common questions
- How many inboxes do I need for cold email?
- Divide your daily sending target by how many emails each inbox should send, and round up. At 30 a day per inbox, 300 cold emails a day needs 10 inboxes and 1,000 a day needs 34. The per-inbox number is your choice; no mailbox provider publishes a safe cold volume, and platforms like Instantly suggest 30 to 50.
- How many inboxes per domain for cold email?
- There is no provider rule. Instantly's guidance is at most 3 to 5 accounts per domain. Fewer inboxes per domain means each domain carries less volume, so a reputation problem on one domain affects a smaller share of your sending, at the cost of buying and maintaining more domains.
- How many cold emails can one domain send per day?
- In this calculator, sends per inbox times inboxes per domain: 30 × 3 is 90 a day. No provider publishes a per-domain cold limit, but Google classifies a domain sending close to 5,000 a day to personal Gmail accounts as a bulk sender, and the calculator warns when you reach that.
- How many cold emails can I send per day from Google Workspace?
- Google's hard limit is 2,000 messages per user per day, but that is an abuse ceiling, not a cold email target. Most cold email tools advise tens per inbox per day, and Google's guidelines say not to email people who didn't sign up, so there is no officially safe cold number.
- How many new prospects do I need each month?
- Monthly sends divided by the steps in your sequence. 500 a day, five days a week, is about 10,833 emails a month; with a three-step sequence that is about 3,611 new prospects. Replies and bounces end some sequences early, so the real number of new contacts is a little higher.
- How long does warm-up take?
- No mailbox provider publishes a fixed period. Two to four weeks of gradually rising volume is a common rule of thumb for a new cold email inbox, and Instantly suggests at least two weeks before campaigns. Google warns against suddenly doubling volume, so raise it in steps and hold each step for a few days.
- Does using more domains avoid Gmail's bulk sender rules?
- Google counts the roughly 5,000-a-day bulk sender threshold per primary domain, including subdomains, so more inboxes on one domain don't help. Separate domains are counted separately. Either way, authenticating with SPF, DKIM and DMARC is worth doing on every sending domain.
- How do I get emails for cold emailing?
- Build the list from sources that match your ideal customer, such as company websites, professional profiles and B2B data providers, then verify every address before the first send. Our guide to building a B2B email list covers the sources; unverified lists are the usual cause of the bounce problems above.
Sources
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