How many domains do you need for cold email?
Divide your total sends by 40 emails a day per inbox, then by 2 to 3 inboxes per domain. For 50,000 leads over 3 months, that means 19 to 29 domains.
The short answer
- The number of cold email domains you need is total sends, divided by what one inbox sends in your timeline, divided by 2 to 3 inboxes per domain.
- A warmed Google Workspace or Microsoft 365 inbox safely sends 30 to 50 cold emails a day, and 1 to 3 inboxes per domain avoids cluster-level filtering, per Nadav Shanun's May 2026 playbook on Indie Hackers.
- A 3-email sequence to 50,000 leads is 150,000 sends. Over 3 months at 40 a day, that needs 57 inboxes on 19 to 29 domains.
- More domains limit damage when one gets flagged. They add capacity only when every domain is warmed, authenticated and fed a clean list.
The formula for cold email domains
Three numbers set your domain count: how many emails you send in total, how long you have to send them, and how hard you push each inbox. Write it out and the answer stops being a guess.
Inboxes needed = total sends ÷ (emails per inbox per day × working days). Domains needed = inboxes needed ÷ inboxes per domain. Total sends is your lead count times the steps in your sequence, since each follow-up is another email.
The inputs come from a dated source. In The Cold Email Infrastructure Playbook (Indie Hackers, 1 May 2026), Nadav Shanun puts the safe ceiling at "30 to 50 cold emails per day" per warmed inbox. He caps inboxes at "1–3 mailboxes per domain," because more than that triggers cluster-level filtering. The table below uses 40 a day and 22 working days a month.
Domains needed for 50,000 leads on a 3-email sequence (150,000 sends)
40 emails per inbox per day, 22 working days a month.
| Campaign length | Sends per inbox | Inboxes needed | Domains at 3 inboxes each | Domains at 2 inboxes each |
|---|---|---|---|---|
| 1 month (22 days) | 880 | 171 | 57 | 86 |
| 3 months (66 days) | 2,640 | 57 | 19 | 29 |
| 6 months (132 days) | 5,280 | 29 | 10 | 15 |
Per-inbox and per-domain inputs from Nadav Shanun, Indie Hackers, 1 May 2026; checked September 2026. Round inboxes and domains up.
Why 50,000 leads in one month is the wrong plan
The 1-month row needs 57 to 86 domains, and every one needs weeks of warmup first. Shanun's playbook says a new inbox needs 3 to 5 weeks before real campaigns. So a one-month blast is really a two-month project, with most of your spend going on domains you'll use once.
The 3-month plan is the practical middle. You buy about 25 domains, warm 57 inboxes in parallel, and keep a few spare domains ready. When one domain gets flagged, you rotate in a warmed spare instead of stopping the campaign.
What to set up on every sending domain
Register domains that look like your brand, such as a variant spelling or a prefix, never a random string. Set SPF, DKIM and DMARC on each one before any mail goes out. Point the root of each domain at your main website so a curious prospect lands somewhere real.
Then track each domain on its own. Shanun's thresholds are a good alarm: spam complaints under 0.1% and hard bounces under 2%. Past those, providers start throttling, and a domain that keeps sending gets worse.
SalesCrew is our product, and it runs this from one place. The mailbox-pool sender spreads a cadence across your own mailboxes under per-mailbox and per-domain daily caps. A bounce or complaint goes straight to the suppression list, and suppression is re-checked at the moment of sending. The sender and domain registry shows every mailbox with its domain. Seats are unlimited, from $299 a month on the pricing page.
Extra domains without warmup add risk, not capacity
Questions
- How many domains do I need for 50,000 leads?
- About 19 to 29 domains if you send a 3-email sequence to 50,000 leads over 3 months. That is 150,000 sends, or 57 inboxes at 40 a day across 66 working days, spread 2 to 3 inboxes per domain. Stretch the campaign to 6 months and you need 10 to 15 domains.
- Can you send cold email from your main company domain?
- You can, but a separate sending domain protects the one your website, support and billing email run on. A spam flag on your main domain hurts every email your company sends. A lookalike domain keeps cold outreach risk away from it.
- How long before a new domain is ready to send?
- Plan on 3 to 5 weeks of warmup per inbox before real campaigns, per Nadav Shanun's May 2026 cold email playbook on Indie Hackers. His ramp runs 5 emails a day in week 1, 10 in week 2 and 20 in week 3, rising toward 40. Buy domains a month before you need them.
- What happens if one sending domain gets flagged?
- Every inbox on that domain loses deliverability, sometimes for weeks. With 20 domains, one flag takes out about 5% of your capacity. With 2 domains, it takes out half. Retire or rest the flagged domain and let the rest of the program carry the volume.