Build a webhook-driven email pipeline for your AI agent

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. The mental model: an Agent Account is just a grant Before any of the pipeline matters, here's the one abstraction that makes the whole thing simple. An Agent Account is a Nylas grant — it has a grant_id , an inbox, an email address on a domain you own, and it speaks every grant-scoped endpoint you already know: Messages, Threads, Folders, Drafts, Attachments, Calendars, Events, Contacts, Webhooks. There's no OAuth token to refresh, no provider-specific quirks, no separate SDK. If you've built against a connected Gmail or Microsoft grant before, the data plane is identical. Nothing new to learn there. What's different is that the agent is a participant. It has its own address — support@yourcompany