Mailbox ramp calculator
A new mailbox in Sealrep sends 5 emails on its first day and one more each day, up to 25 a day from day 21. Put in your mailboxes, sending domains and target companies, and this calculator shows what they can send each day of the ramp, and when every company can have its first email.
By Naman Jain, founder of SealrepPublished 18 October 2026Last reviewed 12 October 2026
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Plan the first three weeks. It runs in your browser.
The numbers are Sealrep's own sending rules, checked against its code on 2 October 2026. What you type stays on this page. They are the most the mailboxes may send, not a forecast of replies.
- Over the 21-day ramp
- 420emails at most
- Once ramped
- 50emails a sending day
- Every first email by
- Day 17300 companies
- Every email fits by
- Day 33900 emails; follow-ups wait their gap
| Day | Each | All mailboxes | Total |
|---|---|---|---|
| 1 Mon | 5 | 10 | 10 |
| 2 Tue | 6 | 12 | 22 |
| 3 Wed | 7 | 14 | 36 |
| 4 Thu | 8 | 16 | 52 |
| 5 Fri | 9 | 18 | 70 |
| 6 Sat | 10 | no sends | 70 |
| 7 Sun | 11 | no sends | 70 |
| 8 Mon | 12 | 24 | 94 |
| 9 Tue | 13 | 26 | 120 |
| 10 Wed | 14 | 28 | 148 |
| 11 Thu | 15 | 30 | 178 |
| 12 Fri | 16 | 32 | 210 |
| 13 Sat | 17 | no sends | 210 |
| 14 Sun | 18 | no sends | 210 |
| 15 Mon | 19 | 38 | 248 |
| 16 Tue | 20 | 40 | 288 |
| 17 Wed | 21 | 42 | 330 |
| 18 Thu | 22 | 44 | 374 |
| 19 Fri | 23 | 46 | 420 |
| 20 Sat | 24 | no sends | 420 |
| 21 Sun | 25 | no sends | 420 |
Why a new mailbox starts at 5, and how fast it climbs.
Mail providers judge a new sender by how it behaves over its first weeks. Gmail asks senders to increase volume slowly and to send at a steady rate rather than in bursts.[1] So each mailbox you connect starts at 5 sends on its first day and gains one a day: 10 on day 6, 15 on day 11, 25 from day 21 on.
Days count from the day you connect the mailbox, weekends included, so one connected on a Friday is already on day 4 by Monday. 25 a day is the ceiling for every mailbox: you can set a lower cap on one, never a higher one. Reconnecting a mailbox keeps its place on the ramp.
Three limits that shape the numbers.
- The sending-domain cap. All your mailboxes on one domain together send at most 3 times one mailbox's cap: 15 a day on day 1, 75 once ramped. A 4th mailbox on the same domain adds nothing, so the calculator spreads mailboxes over the domains you enter and shows any that would sit idle. Sealrep warns you when you connect a 4th mailbox on one domain.
- The campaign window. Campaigns send on weekdays, 08:00 to 17:00 in each recipient's own time zone, unless you change the window. If yours includes weekends, tick the box in the calculator.
- Pacing per company. One first email per company a day, so two people at one company never get a first email on the same day, and at most 3 campaign emails a day to one email domain. With one contact per company, neither slows the plan down.
Every follow-up uses a send from the same daily cap, which is why the calculator asks how many emails each company gets. It also cannot see your list: a mailbox uses at most 50% of its cap on companies whose mail runs on Microsoft 365, and 20% on companies behind a mail security gateway, so for a list heavy with either, read the totals as the top of the range.
When a mailbox stops on its own.
A mailbox pauses itself when hard bounces reach 3% of its sends over the last 7 days, counted once it has sent 20. A campaign pauses at 2% hard bounces, counted after 20 sends.
A mailbox also pauses when people who asked to stop (one-click unsubscribes, 'remove me', angry or legal replies) reach 1% of its last 7 days' sends, or 2% of a campaign's, counted after 50 sends. This is not a spam-complaint rate.
A paused mailbox stays paused until someone on your team resumes it, which is one more reason the calculator shows the most a mailbox may send, not what it will.
Two ways to spend four mailboxes.
Example data: worked out with the same arithmetic as the calculator above.
| Topic | 4 mailboxes on 1 domain | 4 mailboxes on 2 domains |
|---|---|---|
| Mailboxes that send | 3 (the 4th adds nothing) | 4 |
| Day 1 | 15 emails | 20 emails |
| Over the 21-day ramp | 630 emails | 840 emails |
| Once ramped | 75 a sending day | 100 a sending day |
| Every first email by | day 16 | day 12 |
| All 1,200 emails fit by | day 31 | day 25 |
Where every fact comes from. Read on 2 October 2026.
- [1]Gmail Help, Email sender guidelines "Increase sending volume slowly", "Send email at a consistent rate."
- [2]Microsoft Learn, Exchange Online limits recipient rate limit, 10,000 recipients per day.
Spot a mistake? Email hi@sealrep.com and we will correct it within 5 business days.
Questions people ask. Answered straight.
how many cold emails can one mailbox send a day?
In Sealrep, 5 on its first day, rising by one a day to 25 from day 21, and 25 is the ceiling. Microsoft lets a Microsoft 365 mailbox send to up to 10,000 recipients a day,[2] so the limit a new sender meets first is reputation, not the provider's cap.
should I add more mailboxes to send more?
Up to 3 per sending domain. Past that, the mailboxes on one domain share a cap of 3 times one mailbox's, so another one there adds nothing. A second sending domain spreads the load and protects the first.
does the ramp start again if a mailbox pauses?
No. The ramp counts days from when the mailbox was first connected, and pausing or reconnecting it keeps its place.
does Sealrep warm up mailboxes?
No. Sealrep does not sell or warm mailboxes. It sends real emails slowly from mailboxes you already own, inside the ramp above, and checks the domain before a campaign can start.
is anything I type sent anywhere?
No. The calculator is arithmetic in your browser: nothing you enter leaves the page.
Sealrep runs these checks on every draft and mailbox.
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- Nothing sent until you approve
- Domain checked before a campaign starts
- You send on LinkedIn, X and Reddit
Lab only · stands in for the hero and the sections after it; the pill appears once the hero buttons have gone
Get paying clients, not just leads.
Sealrep finds your buyers, drafts your cold email, LinkedIn, X and Reddit outreach, sorts every reply, and offers your booking link.
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- Cold emailResearched emails from your own mailbox, after you approve.
- LinkedInNotes and comments drafted for you to send.
- XReplies and DMs drafted for you to send.
- RedditFinds the threads your buyers are in. You post; it drafts.
- AI searchTracks how AI engines answer about you.
- Reply agentReads every reply, sorts it, and drafts the answer.
- Lead dataNamed companies with the reason they fit.
- Your mailboxesDomain checked, ramped slowly, paused on bounces.
- Browser extensionReads the page when you click, drafts what to say.