What is Secondary sending domain?

A secondary sending domain is a separate domain, usually a close variant of the main one, used only for outbound email so that reputation problems cannot reach the main domain.

Also called: cold email domain, lookalike domain.

If example.com is the company's main domain, a team might send cold email from getexample.com or examplehq.com. Replies still reach a real person, but the domain's sender reputation is separate: a bad week of bounces or complaints there does not push invoices and customer mail from the main domain into spam.

A secondary domain needs the full setup of a real one: SPF, DKIM and DMARC, MX records so replies arrive, and ideally a simple website or a redirect to the main site so a curious prospect finds the company. It also needs warm-up like any new domain.

Volume is usually spread across several domains and several inboxes per domain, each sending a modest number per day. The number you need follows from the emails a campaign requires.

The cold email calculator works out inboxes and domains from a meetings target, and the SPF, DMARC and MX checker confirms each new domain is set up before it sends.