Most "AI email agent" demos send one email and call it a feature. The agent drafts a reply, fires it off, the screenshot looks great. What the demo never shows is the agent in a for loop — working a backlog, fanning out a digest, chasing a list of stragglers — quietly racking up sends until it trips a daily quota and gets a wall of 429s mid-task. Now half your batch went out, half didn't, and the agent has no idea which half.
That failure mode is the whole problem with letting a model decide how fast to send. A human glances at "Send" and pauses. An agent doesn't pause; it has a task list and a tool, and it will happily call that tool two hundred times in a minute. So the fix isn't smarter prompting. It's a backstop in your own code: a throttle that paces sends under the documented ceiling, a queue that holds the overflow, and a backoff loop for the rare 429 that slips through anyway.
Let me be precise about who enforces what, because it's easy to oversell this. Nylas enforces the cap. Your backstop's only job is to keep you from reaching it — to turn a hard 429 wall into a smooth, self-paced drip. I work on the Nylas CLI, so every terminal command below is one I've run against nylas v3.1.27, and every endpoint is checked against the Agent Account usage limits doc.
