Mail providers judge a new address by its history. An address with none is the profile of a spammer, so its first cold emails land in spam no matter how good they are. Warming gives the address a history: steady, two-way conversation over several weeks before the first real send.
Buzzlist treats a mailbox as ready when its provider is active and it is either pre-warmed or has completed at least 20 warm-up sends. Until then, nothing goes out from it.
Warming never stops. A warmed mailbox keeps a slow trickle of normal mail alongside outreach, and the daily cap stays at 20 cold emails so the ratio never looks like a blast.
