How warmup works (and the recommended ramp)

Warmup builds sending reputation for a new or dormant mailbox by generating small, growing volumes of genuinely engaged email before real campaigns run through it. Toggle it per mailbox from the Mailboxes list; a progress bar shows where each mailbox sits on its ramp.

What actually happens

While warmup is on, the scheduler sends a controlled number of messages each day from your mailbox to a peer network of other warming mailboxes. Each peer's own mailbox is checked for the message and it is genuinely marked read, and a portion of confirmed reads get a real reply — the strongest positive signals a sender can accumulate. This only happens between peers whose reply access we've verified; a message that never shows up in the peer's inbox (for instance, landing in spam) is not counted as opened. Volume follows a current_daily_volume → target_daily_volume ramp, advancing roughly 10–20% per day with natural day-to-day variation, and sends are spaced through business hours rather than fired in bursts.

The default ramp

Campaign sends are gated by warmup status: a mailbox in its first week won't be selected by the send governor even if it's in a launched campaign's pool. As the ramp advances, the mailbox's campaign allowance grows into the space under its daily limit. After the ramp completes, keep warmup on — a 10–15% floor of engaged traffic keeps the reputation cushion healthy.

Controls and status

• Start / stop warmup from the mailbox row or detail page. Stopping mid-ramp pauses progress; a stop longer than about two weeks restarts the ramp partway back, because reputation decays.
• Status shows the stage (Seed, Build, Blend, Working, Maintain), today's warmup send count, and engagement rate from the peer network.
• Target volume is editable per mailbox. Raising it extends the ramp; the scheduler never jumps.

For the reasoning behind the numbers, see the blog post Mailbox warmup: the ramp schedule that actually works.