Never send cold email from your primary company domain. If placement goes wrong you have damaged the domain your website, your invoices and your existing customer conversations depend on, and domain reputation is slow to repair.
So you buy separate sending domains. How many, which ones, and named how, turns out to matter considerably more than most people assume.
How many
Work backwards from volume.
Three mailboxes per domain is the advised ratio. Five is the practical ceiling. More concentrates too much sending on one domain’s reputation, and a single problem takes out everything on it.
Per-mailbox daily volume depends on your infrastructure but 30 to 50 cold sends a day is a reasonable planning figure once warmed.
So:
| Monthly sends | Mailboxes | Domains (at 3 each) |
|---|---|---|
| 10,000 | ~8 | 3 |
| 30,000 | ~25 | 9 |
| 100,000 | ~80 | 27 |
| 300,000 | ~240 | 80 |
Buy slightly more than you need. Domains cost $8 to $14 a year and warming takes three to four weeks, so having a couple ready is cheap insurance against needing capacity you cannot conjure quickly.
TLD selection
The TLD affects placement more than people expect, because filters use it as one signal among many.
Safe: .com first, always. .co and .net are fine. Country TLDs matching where you genuinely operate — .co.uk, .de, .com.au — are fine and can help regionally.
Usable with care: .io, .ai, .app. Common in tech and generally accepted, though occasionally treated with more suspicion than .com.
Avoid: the cheap TLDs heavily used for spam. .xyz, .top, .club, .online, .site, .icu and similar. They are cheap for a reason, and some filters penalise them outright regardless of how the domain behaves.
Avoid: anything free.
The rough rule: if a TLD costs under about $5 a year, the spam volume on it is why.
Naming
This is where most estates give themselves away.
Good patterns:
- Add a word to your brand:
getnorthgate.com,trynorthgate.com,northgatehq.com - Use a hyphenated version:
northgate-analytics.com - Use a different TLD for the same brand:
northgate.ioif your main isnorthgate.com - Use a product or division name you actually use
Bad patterns:
- Numbers:
northgate1.com,northgate02.com— transparently a fleet - Random strings:
ngtemail7.com - Anything with “mail”, “send”, “outreach”, “campaign” in it
- Unrelated words that mean nothing to a recipient
The test is simple: if a prospect looked up the domain, would it make sense? They occasionally do, and a domain that clearly exists only to send cold email undermines the message before it is read.
Put something at the domain, too. A single page that redirects to your main site, or a minimal landing page. A domain with no web presence at all is a small negative signal and takes ten minutes to fix.
Age
New domains carry no history. Ideally buy a few weeks before you need them, let the DNS settle, then warm.
Aged domains bought from marketplaces are a mixed proposition. A domain with clean history helps; a domain with a spam history is worse than a new one and the history is not always visible. If you buy aged, check it against blocklists and look at what was previously hosted there before you build on it.
Realistically, buying new and warming properly is simpler and the three-week wait is not the bottleneck people think it is.
Before the first send
Per domain, in order:
- SPF, within the ten-lookup limit
- DKIM, 2048-bit
- DMARC, published, with a reporting address someone reads
- MX, so replies arrive
- Custom tracking domain with valid SSL — a subdomain of the sending domain, not a shared platform tracker
- Something at the root — a redirect or a simple page
- Verify all of it with a check rather than assuming setup succeeded
- Warm for three to four weeks before any real volume
At three domains this is an afternoon. At thirty it is a project, and it is where authentication errors creep in silently. Automated configuration stops being a convenience somewhere around fifteen domains.
Rotation and retirement
Estates are not static.
Rotate gradually. Adding new domains over time and retiring old ones keeps average domain health up without a sudden change in your sending pattern.
Retire a domain when it is blocklisted repeatedly, placement is consistently worse than the rest of your estate, or its bounce history is poor. Do not keep trying to rehabilitate a bad domain when a new one costs $11.
Do not retire everything at once. A wholesale switch looks like exactly what it is.
Never reuse a domain across clients if you are an agency. The reputation belongs to the previous sending behaviour.
Ownership
Briefly, because it has its own piece, and because it is the part with the longest consequences.
Register domains in your own name, on an account you control. If an agency or provider registers them for you, the warmed reputation is theirs and you start again when the relationship ends. Six to ten weeks of rebuilding, against a portfolio worth perhaps $150 a year.
Ask the question before you sign anything.
The short version
Never send from your primary domain. Plan three mailboxes per domain, five at most, and buy slightly more than you need because warming takes weeks.
Stay on .com, .co, .net or a country TLD you genuinely operate in, and avoid the cheap TLDs that spam volume has poisoned. Name domains as plausible variants of your brand rather than numbered fleets, and put something at the root.
Authenticate everything, verify rather than assume, warm for three to four weeks, and rotate gradually rather than wholesale.
And register them in your own name.
Next: how many mailboxes you need, or domain rotation.
Frequently asked questions
How many domains do I need for cold email?
Divide your mailbox count by three. A programme sending 30,000 emails a month needs roughly 25 mailboxes and nine domains. Five mailboxes per domain is the ceiling.
What is the best TLD for cold email?
`.com` first, with `.co`, `.net` and country TLDs matching where you operate also fine. Avoid cheap TLDs heavily used for spam such as `.xyz`, `.top` and `.club`, which some filters penalise regardless of behaviour.
Should I buy aged domains for cold email?
Usually not worth it. A clean aged domain helps slightly, but spam history is not always visible and a poisoned domain is worse than a new one. Buying new and warming for three to four weeks is simpler.
Can I use my main company domain for cold email?
No. If placement goes wrong you damage the domain your website, invoices and customer conversations rely on, and domain reputation is slow to repair.