Warmup is manufactured sending history. Mail providers score senders on track record — volume patterns, engagement, complaints — and a new inbox has none, which itself is suspicious. Warmup builds that record deliberately before real recipients are involved.
What actually happens during warmup
The inbox sends small, slowly increasing volumes (typically starting single-digit daily) to addresses that open, reply, and rescue messages from spam — nowadays usually a warmup network operated by your sending platform. The engagement teaches filters that mail from this sender is wanted.
Our planning numbers, and the reasoning
- 14 days minimum before any real cold volume; 21–30 when the list is valuable. Rushing saves days and risks the domain — bad trade.
- Keep warmup running alongside live sending, at reduced volume — it keeps positive engagement in the mix.
- Watch the warmup dashboard for spam-folder placements; a rising rate is the earliest smoke you’ll get.
Honest caveat: warmup networks simulate engagement, and providers know they exist. Warmup is necessary, not sufficient — it can’t rescue bad lists or spammy copy, and skipping it can’t be compensated for afterward.