if your agent sends email, what sits between the agent and the actual send?

asking people who have agents sending mail in production, not demos. human outbound tools have a schedule baked in — x per mailbox per day, ramped over weeks — because a human sdr sends like a human. an agent doesn't. it sends when something fires, so it's nothing for an hour and then 200 in ten minutes. so what's between "agent decided to send" and the smtp call? - do you rate-limit or queue it yourself, and where did those limits come from? - does anything look at the domain first, or does it just go? - has a burst ever visibly changed where the mail landed, or is this a thing people talk about more than they hit? i've seen this framed as an obvious problem, and i've also seen people say an agent sending isn't meaningfully different from any other automated sender. i can't tell which is true from the outside, so: has anyone actually hit it?