Domains = daily cold emails ÷ (cold emails per mailbox × mailboxes per domain). Plan 10 to 20 cold emails per mailbox per day (15 by default) and 5 mailboxes per domain, so each domain carries 50 to 100 cold emails a day (75 at the default). 750 cold emails a day ÷ 75 = 10 domains holding 50 mailboxes, which is exactly a Winnr Startup plan. Use at least a few domains even at low volume, so one problem can't stop everything.
Never send cold email from your main business domain. If its reputation suffers, invoices, support replies and every other email your company sends suffer with it. So cold email runs on separate sending domains, and the question becomes how many. Too few and each one carries too much volume; too many and you pay for and manage domains you don't need.
| Cold emails/day | Mailboxes | Domains | Domain cost (one-time) | Per domain/day |
|---|
Mailboxes are rounded up first, then domains. Winnr domains are a one-time purchase priced by extension. Plan mailboxes: Startup includes 50, Enterprise 200, extra mailboxes are $1/month each. For plan cost, warming and the full picture, use the cold email calculator.
The math, step by step
- Mailboxes = daily cold emails ÷ cold emails per mailbox, rounded up. At 15 a mailbox, 750 a day needs 50 mailboxes.
- Domains = mailboxes ÷ mailboxes per domain, rounded up. At 5 per domain, 50 mailboxes need 10 domains.
That gives a per-domain load you can check:
| Cold emails per mailbox | Mailboxes per domain | Cold emails per domain per day |
|---|---|---|
| 10 (safe) | 5 | 50 |
| 15 (default) | 5 | 75 |
| 20 (upper limit) | 5 | 100 |
So the "50 to 100 cold emails per domain per day" figure you'll see elsewhere on this site isn't a separate rule. It is simply 5 mailboxes × 10 to 20 cold emails each. If you put fewer mailboxes on a domain, its load drops with them. Each mailbox should also stay at 50 or fewer emails a day in total once warming is counted.
What domains cost
Domains bought through Winnr are a one-time purchase, priced by extension and shown in the search results before you select anything. A .com is about $13. The Classic purchase registers .com, .co, .org and .net; premium .io, .sh, .vc and .to are available through the Subdomain Strategy. Domains you already own connect for free, and Enterprise includes 5 free domain purchases. Cold email domains covers buying, connecting and DNS in one place, and best TLDs for cold email explains which extension to pick.
Domain slots aren't a paid limit either: Startup starts with 10 and Enterprise with 40, and you can raise the count yourself in Settings, Subscription.
Why the domain count matters
- Risk spreading. If one domain has a problem, the others keep sending. With 10 domains, one burned domain costs you a tenth of your capacity, not all of it.
- Per-domain volume. Filters judge each domain on its own pattern. Keeping each one to 50 to 100 cold emails a day keeps that pattern modest.
- Reputation isolation from your main domain, which should never send cold email at all.
- Room to rotate. Spare domains let you move volume the day something goes wrong.
One domain or many?
| One sending domain | Several sending domains | |
|---|---|---|
| Suits | Very low volume (up to about 100 cold emails a day across 5 mailboxes) | Anything above that |
| Setup | Simplest | More domains to buy and check, though Winnr sets up DNS on each automatically |
| Risk | One problem stops everything | One problem affects only that domain's mailboxes |
Even at low volume, two or three domains are cheap insurance. At any real scale, plan on many.
Subdomains: when they work and when they don't
Don't send cold email from subdomains of your main business domain (outreach.yourcompany.com). Domain blocklists list the registered domain, so a problem on that subdomain can reach your main domain.
Subdomains of a dedicated sending domain are a different matter. Winnr's Subdomain Strategy registers one apex domain used only for cold email and puts up to 5 subdomains under it, each a full email domain with its own MX, SPF, DKIM and DMARC and up to 10 mailboxes. You register far fewer domains, on .com, .net, .org, .co or a premium low-abuse extension (.io, .sh, .vc, .to). The trade-off is concentration: a listing on the apex affects every subdomain under it. It is an alternative shape, not the default.
Domain best practices
- Authenticate every domain with SPF, DKIM and DMARC. Winnr publishes them automatically, with DMARC at
p=reject. - Warm every new mailbox for at least 2 weeks before cold sending, 4 on a brand-new domain. Built-in warming is $0.60 per mailbox per month.
- Need to start sooner? Pre-warmed domains come aged, with mailboxes already warmed, at $3 per address per month. See aged vs new domains for when it's worth it.
- Spread volume evenly across domains and mailboxes, and send steadily every day rather than in bursts.
- Point each sending domain at your website with a domain redirect, so anyone who checks it sees a real business.
- Watch each domain: bounces, complaints, replies and occasional seed tests.
Naming your domains
- Brand variations: getacme.com, tryacme.com, acmehq.com, acme-team.com.
- Brandable invented names that don't share a spam-filter fingerprint with your real brand. Winnr's domain search generates these by default.
- Avoid look-alikes of other companies' brands, hyphens everywhere, numbers that look like letters, and cheap TLDs.
Worked examples
| Target | Mailboxes (at 15 each) | Domains (at 5 each) | Winnr plan |
|---|---|---|---|
| 300 cold emails/day | 20 | 4 | Startup ($69, includes 50 mailboxes) |
| 750 cold emails/day | 50 | 10 | Startup ($69) |
| 1,000 cold emails/day | 67 | 14 | Startup + 17 extra mailboxes ($86) |
| 3,000 cold emails/day | 200 | 40 | Enterprise ($189, includes 200 mailboxes) |
Add a buffer of 10 to 15% spare mailboxes to rotate in. Domain purchases are extra and one-time; see Winnr pricing for the plans.
When to add more domains
- Your mailboxes are at the top of the 10 to 20 range and you need more volume.
- A domain is burned or paused and its load has moved onto the others.
- You're starting campaigns for a new market or client and want them separated.
Each new domain needs its mailboxes warmed before it carries cold email, so add capacity a few weeks before you need it, or use pre-warmed domains to fill the gap.
Frequently Asked Questions
How many domains do I need for cold email?
Divide your daily cold email target by the cold emails each domain carries. At 5 mailboxes per domain and 15 cold emails per mailbox, each domain carries 75 a day, so 750 cold emails a day needs 50 mailboxes on 10 domains.
How many mailboxes should I put on each domain?
5 is the recommendation, and Winnr allows up to 10. At 10 to 20 cold emails per mailbox, 5 mailboxes means 50 to 100 cold emails per domain per day.
How many cold emails can one domain send per day?
Plan 50 to 100: 5 mailboxes sending 10 to 20 cold emails each, 75 at the default of 15. Keep each mailbox at 50 or fewer emails a day in total once warming is counted.
Should I use subdomains or separate domains?
Never subdomains of your main business domain. Separate sending domains are the default. Subdomains of a dedicated sending domain, as in Winnr's Subdomain Strategy, are an alternative that needs fewer registrations but concentrates risk on one apex.
What do domains cost on Winnr?
Each domain is a one-time purchase priced by extension, shown before you buy; a .com is about $13. Connecting domains you already own is free, and Enterprise includes 5 free domain purchases.
Related guides: Best TLDs for cold email, the Subdomain Strategy, cold email best practices and SMTP vs Google Workspace vs Microsoft 365.