How to Set Up Domains and Inboxes for Cold Email

Most cold email problems start before the first email is written. If your domains and inboxes are set up badly, good copy still ends up in spam.

Here's the setup we'd recommend to any founder or small sales team: separate sending domains, the right number of inboxes, correct DNS records, and a slow ramp. It takes an afternoon, then a few weeks of warmup.

Don't send cold email from your main domain

Your main domain (say, acme.com) carries your company email: invoices, password resets, customer support, investor updates. If cold outreach damages its reputation, all of that mail starts landing in spam too.

Cold email is riskier than normal mail. Some people will mark it as spam, some addresses will bounce, and a bad week can drag a domain down. Keep that risk on domains you can afford to rest or retire.

The fix is simple: buy a few lookalike domains that clearly belong to your brand and send all cold outreach from those.

Picking lookalike domains

A good sending domain is obviously yours to a human reader and not trying to trick anyone. Common patterns:

A few rules that keep you out of trouble:

• Stick to .com when you can. Unusual TLDs (.xyz, .top, .info) are cheap for a reason and are often associated with spam.
• Avoid hyphens and numbers. acme-mail.com and acme1.com look less trustworthy.
• Never use misspellings. acrne.com (r-n instead of m) looks like phishing, because that is what phishers do.
• Keep the brand recognizable. If a prospect can't tell the domain belongs to your company, they're less likely to reply.

Forward the lookalike domain to your main site

Prospects will check who you are. If getacme.com shows an error page, it looks shady.

Set up a 301 redirect from each sending domain to your main website. Most registrars have a "domain forwarding" setting that takes two minutes. Forward the root and the www version.

How many inboxes and domains you need

Most people guess. Do the math instead.

A common rule of thumb is 30 to 50 cold emails per inbox per day once the inbox is warmed up. It's a conservative starting point, not a hard limit, so start at the low end. Pair it with 2 to 3 inboxes per domain so no single domain carries too much volume.

Worked example

Say you want to reach 2,000 new prospects a month with a 4-step email sequence.

1. Total emails: 2,000 prospects × 4 steps = 8,000 emails a month (an upper bound, since replies stop the sequence).
2. Per day: 8,000 ÷ 22 business days ≈ 360 emails a day.
3. Inboxes needed: 360 ÷ 30 per inbox = 12 inboxes. At 50 per inbox it would be about 8. Plan for the conservative number: 12.
4. Domains needed: 12 inboxes ÷ 3 per domain = 4 domains.

So the setup is 4 domains with 3 inboxes each, plus one spare warmed-up domain if you want something to swap in when a domain needs a rest.

The same math at other volumes:

If you want more volume, add inboxes and domains. Don't push each inbox harder.

SPF, DKIM and DMARC, explained simply

These three DNS records prove to receiving mail servers that you're allowed to send from your domain. Without them, much of your mail gets rejected or filtered, and Google and Yahoo's sender rules expect them. Every sending domain needs its own set, added at your registrar or DNS host.

SPF: who is allowed to send

SPF is a TXT record on the root of your domain listing which mail services may send for it. Only have one SPF record per domain.

For Google Workspace:

Type: TXT
Host: @
Value: v=spf1 include:_spf.google.com ~all

For Microsoft 365 (Outlook):

Type: TXT
Host: @
Value: v=spf1 include:spf.protection.outlook.com -all

DKIM: a signature on every email

DKIM signs each message so the receiver can confirm it really came from your domain and wasn't altered. You generate the key in your email provider, then publish it in DNS.

For Google Workspace it's a TXT record (the key comes from the Admin console):

Type: TXT
Host: google._domainkey
Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqh...(long key from Google)

Microsoft 365 uses two CNAME records instead (selector1._domainkey and selector2._domainkey), shown in the Defender portal. After publishing, switch DKIM signing on inside the provider.

DMARC: what to do when checks fail

DMARC tells receivers what to do with mail that fails authentication, and where to send reports. Start in monitoring mode:

Type: TXT
Host: _dmarc
Value: v=DMARC1; p=none; rua=mailto:dmarc@getacme.com

Once you've confirmed everything passes for a few weeks, you can tighten it to p=quarantine. Don't jump straight to p=reject on a brand new domain.

Confirm all three records pass before you send anything. SuperSend checks SPF, DKIM and DMARC on every connected domain and flags anything missing.

Warmup and ramp

A brand new inbox has no sending history. If it sends 50 cold emails on day one, it looks exactly like a spammer.

Warmup fixes this by having the inbox send and receive a small, growing number of normal emails that get opened and replied to. Turn it on the day you create the inbox and leave it running.

Then ramp cold volume slowly. A common starting schedule:

This is a guide, not a guarantee. If bounces climb or replies dry up, hold volume or step back a week.

During the ramp, also:

• Verify your list. Sending to bad addresses is the fastest way to hurt a new domain. Keep bounces low.
• Keep first emails plain. Text only, few or no links, no images or attachments.
• Set up each inbox like a real person. First and last name, a profile photo, and a simple signature.

For everything to check before and after launch, see the cold email deliverability checklist.

Google Workspace vs Outlook

Most cold email inboxes run on Google Workspace or Microsoft 365. Both work, and many teams run a mix.

Why mix? Your prospects use both, and many senders find same-provider mail (Google to Google, Outlook to Outlook) lands a little better, though that varies. A mix also means one provider changing its filtering doesn't hit your whole setup at once.

A practical approach:

• Default to Google Workspace if you're selling mostly to startups and tech companies, which skew toward Google.
• Add Outlook inboxes if you sell into larger or more traditional companies, which often run on Microsoft 365.
• Not sure? Start with roughly two thirds Google and one third Outlook, then compare reply rates by sender after a month.

Setup checklist

Use this for every new sending domain:

• Buy a lookalike .com domain (no hyphens, numbers or misspellings)
• 301 redirect it to your main website
• Create 2 to 3 inboxes with real names, photos and signatures
• Add one SPF record
• Generate and publish DKIM, then turn signing on
• Add a DMARC record starting at p=none
• Confirm all three records pass
• Turn on warmup and leave it on
• Ramp cold volume over 3 to 4 weeks
• Verify every list before it goes into a sequence

You can buy Google or Outlook inboxes ($5/month each) and domains ($13/year) directly inside SuperSend, or connect the Google Workspace and Outlook inboxes you already have. Warmup is included on every inbox. Using the worked example above, 12 inboxes and 4 domains would come to $60 a month plus $52 a year.

Once the inboxes are warm, put them to work in a follow-up sequence that rotates across all of them.

The short version

• Never send cold email from your main domain. Use lookalike domains like getacme.com or tryacme.com and forward them to your site.
• Plan around 30 to 50 cold emails per inbox per day once warm, with 2 to 3 inboxes per domain. Do the math from your monthly volume.
• Every sending domain needs SPF, DKIM and DMARC. Start DMARC at p=none.
• Run warmup on every inbox and ramp cold volume over 3 to 4 weeks.
• A mix of Google Workspace and Outlook inboxes spreads your risk.

Ready to set up your sending domains and inboxes? See SuperSend pricing.