Human-in-the-Loop: Email Approval Workflows for Agents

The most effective safety control for an email agent isn't a better model, a longer system prompt, or a stricter eval suite. It's a draft folder. Here's the setup. Nylas Agent Accounts — currently in beta — are hosted mailboxes your application creates and controls entirely through the API. Each one is a real address with a grant_id that works against the existing Messages, Drafts, Threads, and Folders endpoints, and each mailbox ships with six system folders: inbox , sent , drafts , trash , junk , and archive . That drafts folder is where your approval workflow lives. Full autonomy is a choice, not a default A common pattern for support mailboxes: an LLM drafts replies to common questions, and humans approve the sensitive ones via a webhook flow. The agent handles the boring 80% on its own — password reset instructions, shipping status, "where's the invoice" — and anything touching refunds, legal language, or an angry customer goes through a person first. The threat you're mitigating is mundane: a model that's confidently wrong. Hallucinated discounts, replies to the wrong thread, a tone-deaf response to a complaint. None of these are exotic attacks. They're the everyday failure modes of putting a probabilistic system on an outbound channel, and the mitigation is to put a deterministic gate between "the model wrote something" and "a customer received it." The gate is three API calls The flow: a message.created webhook fires when mail arrives, your classifier decides the risk level, and high-risk replies become drafts instead of sends. Drafts support full CRUD at /v3/grants/{grant_id}/drafts , so the agent creates one like this: curl --request POST \ --url "https://api.us.nylas.com/v3/grants/ $GRANT_ID /drafts" \ --header "Authorization: Bearer $NYLAS_API_KEY " \ --header "Content-Type: application/json" \ --data '{ "subject": "Re: Refund request for order 4821", "body": "Hi Sam, I have processed the refund...", "to": [{ "email": "sam@example.com" }], "reply_to_mess