Secondary domain
A secondary domain is a separate domain used only for cold email, so that any reputation damage stays away from your main business domain.
If you send cold email from your main domain, a bad campaign can put your normal business mail in spam too, including invoices and replies from customers. A secondary domain keeps the risk apart. You buy a domain that is close to your brand, such as a different ending or a short added word, and send cold email from mailboxes on that domain.
Set it up like any sending domain: mailboxes at a real provider, MX records, SPF, DKIM and DMARC, and a redirect from the domain to your main website so a curious prospect finds you. Warm up each mailbox before real campaigns.
Do not put too many mailboxes on one domain. Spread them out, with only a few per domain, and use more domains as you grow. A secondary domain does not remove the need for good lists and good copy. If you burn the domain, you lose only the domain, but you also lose the work you put into it. Treat it as protection, not as permission to send badly.