Reputation here is a number about your agent, computed from what actually happened to its mail — replies, bounces, complaints and suppression hits — over a rolling 30 days. It is isolated per workspace: nothing another customer does moves your score, and nothing you do moves theirs.
Pools
A send is routed to a pool based on that score and the message's own classification. A clean agent sending transactional mail takes the clean pool. An agent whose recent mail has been marginal is routed away from it, which protects everyone else on the rail — including the rest of your own agents.
Reading it
The Overview page shows reputation, current pool, bounce rate and complaint rate with their limits. GET /v1/reputation returns the same per agent, and the MCP server exposes it as a tool so an assistant can check its own standing before it sends.
How to keep it high
Send to addresses that asked to hear from you. This is the whole game.
Respect bounces — the suppression list does this for you if you let it.
Split agents by job, so a noisy notification stream cannot drag down the mail your customers actually reply to.
Do not test against a single address thousands of times; it teaches filters exactly the wrong thing about your domain.