What is IP pooling?

IP pooling is the practice of grouping multiple IP addresses together for email sending. Messages are distributed across the pool rather than sent from a single IP. ESPs use pools to manage reputation, balance load, and provide redundancy.

Benefits of IP pooling:

Load distribution: Spreading volume across IPs prevents any single IP from exceeding rate limits or appearing to send unusually high volumes.

Reputation averaging: The pool's collective behavior determines reputation. Good senders in the pool help offset occasional issues; bad senders can drag it down.

Redundancy: If one IP gets blocklisted, traffic shifts to clean IPs while the issue is resolved.

ESPs typically maintain multiple pools segmented by sender quality. New or risky senders start in general pools; proven senders may graduate to premium pools with better reputation.

For self-hosted setups, you can create pools using transport maps that randomly or sequentially select from a list of IPs. Commercial MTAs like PowerMTA have built-in pool management with sophisticated selection algorithms.

A pool is a fleet, not a single ship. The convoy's reputation depends on all vessels, so pool operators actively police sender behavior.