What is Email warmup?
Sending ordinary emails between real inboxes that open, reply and rescue them from spam, so a new mailbox builds sending reputation before cold outreach begins.
A mailbox provider decides where to deliver your email partly on how recipients have treated mail from that address and domain before. A new mailbox has no history. Warmup manufactures a good one: the mailbox exchanges messages with other warmed inboxes that open them, mark them not-spam if they landed there, and reply to a share — the engagement signals providers score.
Warmup should run for one to three weeks before the first cold send, then continue permanently at a steady level, because reputation decays without engagement. Typical steady volume is 20–30 warmup emails a day per mailbox.