Most "AI email" tutorials end with a while True loop that polls an inbox every thirty seconds, runs the new messages through a model, and sends a reply. It demos fine. Then you put it in front of real traffic and the cracks show up immediately: you're burning API calls to fetch nothing 99% of the time, your reaction latency is bounded by your poll interval, and the moment you scale to more than one inbox the polling cost multiplies.
Polling an agent's inbox is wasteful. Webhooks are the right primitive for this. The mailbox already knows the instant a message lands — there's no reason to keep asking. What you actually want is a pipeline: inbound mail fans out to a verified ingest endpoint, lands on a queue, and gets picked up by workers that drive your agent runtime and send the reply. This post is about that architecture end to end — not a single feature, but the whole flow, with the parts that bite you in production (idempotency, retries, ordering, backpressure) called out honestly.
I work on the Nylas CLI, so the terminal commands below are the exact ones I reach for when I'm wiring this up. I'll show the curl HTTP call and the CLI equivalent for every concrete step, because you'll use both: curl in your provisioning scripts, the CLI when you're poking at a live account.
