What is IP/domain warming after migration?

After migrating to a new ESP with new IPs, you need to warm those IPs before sending at full volume. Warming establishes reputation through demonstrated good behavior.

Why warming is necessary:

New IPs have no history; mailbox providers are suspicious

Sudden high volume from unknown IPs looks like spam

Gradual increases with positive engagement build trust

Warming approach:

Week 1: Send to your most engaged subscribers only (opened/clicked recently)

Week 2-3: Gradually expand to moderately engaged

Week 4+: Continue expanding based on performance

Volume increases might be: 1,000 → 5,000 → 15,000 → 50,000 → 100,000+ over several weeks

Monitoring during warmup:

Watch bounce rates (should stay low with engaged recipients)

Monitor complaint rates (similarly low)

Check inbox placement with seed testing

Review ESP delivery metrics closely

Slow down if metrics degrade

Domain warming:

If using new sending domains, they need similar gradual introduction

New subdomains of established domains inherit some trust

Brand new domains face extra scrutiny

Your ESP may provide warming schedules or automated warming tools. Follow their guidance while monitoring your specific results.