IP Warm-up

Warm-up is the process of establishing sending reputation on a new IP or domain. The mechanism is simple: mailbox providers watch how recipients respond to your first sends and use that behaviour to inform how they treat later sends. If your first sends produce engagement, subsequent volume is accepted. If they produce complaints or bounces, subsequent volume is throttled or filtered.

Segment first, volume second

The single most important warm-up decision is who to send to on day one. Send your most engaged segment — recent openers, active customers, transactional recipients — before touching any inactive segment. A new IP that starts with high engagement warms in 2–3 weeks. A new IP that starts with a broad blast to a stale list rarely recovers.

Volume curves

A typical curve starts at 50–200 messages per major provider on day one, doubles roughly every 2–3 days, and stabilises at target volume over 14–28 days. Curves for target volumes above 5M/day take longer. Curves that stall are a signal to pause and diagnose, not to push through.

Signals to watch

• Postmaster domain and IP reputation trending up, not down
• SNDS status green
• Complaint rate below 0.05% at every provider
• Defer rate at each provider below 5%
• Bounce rate below 2%

When to stop and reset

If reputation stalls at Medium (Postmaster) or Yellow (SNDS) for a week without improvement, do not increase volume. Investigate the segment, content or cadence. Sometimes the correct action is to reduce volume for a week and let engagement re-establish. Pushing through a stall reliably ends in Bad/Red status and multiple weeks of remediation.