What is “cold” vs “warm” IP reputation?

IP temperature describes the state of an IP's sending history and reputation with mailbox providers.

A cold IP is new or hasn't sent email recently. It has no established reputation, which makes mailbox providers suspicious. They don't know if this IP belongs to a legitimate sender or a spammer who just acquired fresh infrastructure. Cold IPs face strict rate limits and heavy filtering until they prove themselves.

A warm IP has consistent sending history with positive signals: low complaints, good engagement, clean bounce rates. Mailbox providers trust it based on track record. Warm IPs enjoy higher sending limits and better inbox placement.

IP warming is the process of gradually increasing volume on a cold IP to build reputation. You start with small volumes to your most engaged recipients, slowly scaling up over weeks. This generates positive signals that warm the IP.

Warming schedules vary, but a typical approach:

Week 1: 1,000-5,000 emails/day

Week 2: 5,000-15,000 emails/day

Week 3: 15,000-50,000 emails/day

Week 4+: Continue scaling based on performance

Cold IPs are unknown ships entering port. They're inspected carefully until they establish a record of safe voyages.