Email API for AI Agents: What to Evaluate Before You Pick One

Hook Most developers discover the limits of their email API only after something breaks in production. An agent sends a follow-up reply that lands outside the original thread. An inbound message arrives at a webhook endpoint and disappears with no way to replay it. A compliance audit asks for an audit log that was never generated. By then, migrating to a different provider is painful. Choosing an email API for an AI agent is a different problem from choosing one for transactional email. A welcome email does not need to receive replies. An AI agent does. The decision criteria are not the same, and most comparison guides available today were written with transactional use cases in mind. The Problem The standard comparison framework for email APIs focuses on deliverability, latency, and price per message. Those things matter, but they answer the wrong question for agents. When an agent manages an ongoing support conversation, a sales sequence, or an approval workflow, the relevant questio