Key takeaway: Never send from your primary domain. Buy legitimate looking secondaries, redirect each to your real site, run two to three inboxes per domain, and scale by adding domains, not by pushing inboxes harder.

How many domains? How many inboxes on each? Get this wrong and you either cannot scale or you burn everything at once. Here is the framework.

Rule 1: Never send from your primary domain

Your main company domain is the one your customers, invoices, and support emails depend on. Cold email carries real risk of complaints and reputation damage. The two must never touch. This is non negotiable, and it is the first thing agencies get wrong.

Rule 2: Buy secondary domains that look legitimate

Close variants of your real domain work best: getyourcompany.com, yourcompany-team.com, tryyourcompany.com, or a .co or .io version if it fits your brand. Avoid anything that looks disposable or auto generated. If a recipient would not believe it belongs to a real business, neither will a filter.

Rule 3: Redirect every sending domain to your real site

A domain with no website behind it is a red flag. A 301 redirect to your homepage takes minutes and makes each sending domain look like what it is: a legitimate arm of a real company.

Rule 4: Two to three inboxes per domain

This is the load bearing number. More inboxes on one domain concentrates risk. If that domain gets flagged, every inbox on it goes down together. Spreading thin means a problem stays contained.

Rule 5: Scale by adding domains, not by pushing inboxes harder

The instinct when you need more volume is to send more per inbox. That is exactly what gets you filtered. The correct move is more inboxes across more domains, each sending a modest, human amount.

Doing the math

Work backwards from your target. Per inbox volume is low, so you spread across many inboxes and domains. If you want 1,000 sends a day on Google at up to 15 per inbox, you need roughly 67 inboxes, which at 3 per domain means about 22 domains. On Azure at 2 to 3 per inbox you need more inboxes, which its low cost per inbox makes affordable. Add a buffer, because you will want headroom rather than pushing every inbox to its ceiling.

Isolate by campaign or client

If you run outreach for multiple clients or offers, keep their domains separate. One client's aggressive campaign should not be able to damage another's deliverability. Segmentation costs a little more and saves you from correlated failure.

Plan for attrition

Domains get burned. It happens even to careful senders. Treat domains as consumable infrastructure rather than permanent assets: keep a few warmed and in reserve, rotate them in, and retire anything that has been flagged repeatedly. Domains are cheap. Your time and your reputation are not.

Frostmailer provisions your secondary domains, redirects, and inboxes to this exact shape: two to three inboxes per domain, isolated by client, ready to rotate. You get the architecture right from day one instead of rebuilding it after the first domain burns.

Want this done for you?

Our Build and Release service stands up your entire cold email infrastructure: domains, mailboxes, authentication, warm-up, and tracking, all authenticated and ready to send. You skip the weeks of setup and start with campaigns.

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