Run this before any new domain or mailbox sends cold email. It produces a ramp schedule and a clear go/no-go decision for opening campaign volume.

The play

Separate the asset from the brand: cold email runs on secondary domains, never the company's primary domain. The primary's reputation is not a chip to gamble.
Give a fresh domain two weeks of silence after setup: authentication configured, mailboxes created, signatures and profile pictures in place, zero cold sends. Age is part of reputation.
Warm for at least three weeks before campaign volume: start at a handful of sends per day per mailbox, grow the daily count a little every few days, and keep replies flowing; a mailbox that only sends and never receives looks like a cannon, not a person.
Cap real campaign volume per mailbox at 20-30 cold sends per day, and keep warm-up activity running in the background even after campaigns start. Scale by adding mailboxes and domains, not by pushing one inbox harder.
Go/no-go before launch: spot-check where warm-up messages land. Anything worse than consistent inbox placement means the ramp continues; launching into the spam folder burns the list and the domain together.
On a placement drop or a bounce spike mid-campaign: cut volume in half, hold for several days, and only ramp back one step at a time: the same discipline as the initial warm-up, at smaller scale.

What good looks like

Good operators treat sending volume as something a mailbox earns, week by week; the mediocre version buys a domain on Monday and blasts 200 sends on Friday, then wonders why replies stopped.
The tell that separates experts: they watch placement and bounce rate per mailbox, not per campaign, and they act on the first bad signal instead of the fifth.
Consistency beats speed here exactly as on social channels: identical, boring, daily behavior is what reputation systems reward.
Done well, every mailbox reaches campaign volume with steady inbox placement, bounce rates stay low, and a placement incident costs days, not domains.