Warmup

Warmup has two meanings in email. The first is the legitimate process of gradually building reputation on a new domain or IP — ramping volume over weeks so that ISPs can build positive sender history. Domain warming and IP warming are essential before launching high-volume sends.

The second meaning, often used in cold-email tooling, is the practice of sending fake conversations between mailboxes in a pool to artificially inflate engagement metrics (opens, replies). The theory is that ISPs will see your mailbox in active conversation and improve your reputation. In practice, ISPs are increasingly good at detecting warmup traffic patterns and discount or penalize accordingly.

Legitimate reputation building is structural (real engagement, clean lists, gradual volume ramp). Synthetic warmup is a workaround that has diminishing returns. For new domains, the structural path is the one that scales.