How do IP pools share reputation?

IPs within a shared pool develop a collective reputation. Mailbox providers recognize that neighboring IP addresses often belong to the same infrastructure and treat them as related.

When one sender in the pool generates high complaints or hits spamtraps, the entire pool's reputation suffers. This is why reputable ESPs actively monitor and remove bad actors from their shared infrastructure. They cannot afford to let one customer contaminate the pool for everyone else.

The degree of sharing depends on how providers group IPs. Some evaluate entire /24 subnets (256 addresses) together. Others track narrower ranges or individual addresses based on observed sending patterns.

A shared IP pool is like a fleet sailing under one company's banner. If one ship smuggles contraband, port authorities may inspect the entire fleet more carefully until they confirm which vessels are trustworthy.