Why a cold IP gets throttled
Receivers (Gmail, Outlook, Yahoo) see thousands of new IPs come online every day — most of them spam senders trying to dodge a previous reputation. A fresh IP suddenly emitting high volume looks like exactly that pattern.
Conservative throttling on new IPs (often 50-500 messages per recipient ISP per day for the first week) is the safest receiver behaviour. Until enough engagement data accumulates, the IP stays in the slow lane.
A typical warmup schedule
Week 1: 50-100 messages per day, mostly to engaged recipients (real customers, opt-in subscribers). Send only your highest-quality, highest-engagement content.
Week 2: 500-1000/day, still targeting high-engagement segments.
Weeks 3-4: 5k-10k/day, beginning to mix in broader segments.
Weeks 5-6: Approaching full target volume. By week 6 most IPs are fully warmed against Gmail / Outlook for typical SaaS volumes.
These numbers are baseline; specific receivers may want faster or slower ramps depending on engagement signals.
What kills a warmup
High bounce rate. Sending to outdated lists during warmup is the fastest way to wedge a new IP — bounces on a low-volume IP look much worse than the same bounces on a warmed IP.
Complaint spikes. A single bad-looking campaign in the warmup window can collapse the carefully-built reputation.
Volume jumps. Going from 100/day to 10k/day overnight looks suspicious; ISPs throttle the spike and the reputation never finishes building.
How SNDR handles warmup
New customers on the shared MTA pool inherit warmed-IP reputation immediately — no warmup needed for typical send volumes.
Customers who require dedicated IPs (high-volume marketing, regulated industries) get our managed warmup: SNDR routes a fraction of their outbound traffic through the new IP each day, ramping over 4-6 weeks according to engagement signals. The customer dashboard shows ramp progress and per-ISP reputation status throughout.