How to set up your sending infrastructure for cold email (without burning your domain)
Ivona
July 22, 2026
|4 min read
Your infrastructure is the technical foundation of deliverability: your domains, your mailboxes, and how you authenticate and ramp them up. Get this wrong and no amount of good content will save you. Here's how to set it up properly.
Never send cold email from your main domain
This is the single biggest mistake teams make. Your main domain is used for invoices, client communication, and every other part of your business. If it gets burned (flagged as spam by providers), all of that communication breaks too.
Instead, buy a separate domain just for outbound, and point it to your main website. If your outbound domain doesn't redirect anywhere real, that's a red flag for providers too.
How to pick a lookalike domain
A lookalike domain is a variation of your main domain name, used only for sending. Some patterns work well, others will hurt you.
Good patterns:
- Prefix or suffix without a separator: tryacme.com, acmehq.com
- A legitimate TLD swap: acme.io
Avoid:
- Exotic or untrustworthy TLDs (anything obscure or unfamiliar to providers)
- Typosquatting (swapping a letter to look like your real domain, e.g. replacing an "m" with an "n"). This looks like a phishing attempt.
- Numbers in the domain name. They're tempting for branding, but they make cold outreach much harder.
- Separators like hyphens between words.
Before you buy, check if the domain has a bad history. Search "[domain name] blacklist" on Google to see if it was previously flagged.
Let your domain age before you send
Don't send any cold email in the first four weeks after buying a domain. This gives blacklist checks time to clear and lets the domain "cook." The same goes for new mailboxes: don't send anything the first week. Use an answer-only mode that only replies to existing conversations, and let the mailbox warm up for four to five weeks before sending cold outreach.
How many domains and mailboxes do you need?
This comes down to volume and timeline. The target is to stay around 40 emails per day per mailbox (the safe range is closer to 25-35). To figure out how many mailboxes you need:
- 1,000 leads, reaching them within 3 weeks (15 sending days) = about 66 emails per day = at least 2 mailboxes
- 500 leads, reaching them within 1 week (5 sending days) = 200 emails per day = at least 5 mailboxes
As a rule, the more domains and mailboxes you spread your volume across, the lower your limits per mailbox need to be, and the safer your overall reputation stays.
Split across providers
Roughly 80% of the market runs on Google or Microsoft, split close to 50/50 between the two. Don't put all your mailboxes on one provider. Spreading across both protects you if one provider has an issue, and it gives you more combinations when sending to leads on different providers.
The 4-phase ramp-up and limit strategy
- Ramp-up (4-6 weeks): Start with a low daily limit (around 1 to 2 emails) and a ramp-up increment of 1 to 2 emails per day, letting the volume grow gradually.
- Reputation stabilization (1-3 weeks): Keep the mailbox warming up until its deliverability score is consistently above 90.
- Volume switching: Lower the warm-up volume and start sending real campaigns, keeping daily volume under 40 emails per mailbox.
- Ongoing reputation check: Keep a small batch of warm-up-only emails running in the background at all times. These are plain emails with no links, images, or sensitive content, so they're the most likely to land in the inbox. If their spam rate spikes while you're running a real campaign, that's an early signal something in your reputation is going wrong.
Always keep a backup
Keep about 10% of your domains and mailboxes in reserve. If you have 10 domains, keep 1 as backup. If you have 100 mailboxes, keep 10 in reserve. If one mailbox or domain takes a hit, you can switch to a backup immediately instead of going into panic mode while you fix the original.
The bottom line
Infrastructure isn't a one-time setup, it's an ongoing system: separate domains, smart lookalikes, patient aging and warm-up, the right number of mailboxes for your volume, provider diversity, and backups ready to go. Get this right first, because no warm-up routine or content strategy can fix a domain that was set up wrong from the start.
Product Marketing Manager
