Give Your AI Agent Its Own Inbox: A 5-Minute Setup with MCP

Most email APIs are send-only. But if you're building an agent that needs to have a conversation over email — support, scheduling, invoicing — it needs to receive replies too, with thread context. In this post we'll set up an agent with its own mailbox using the Model Context Protocol. This is an official EngageLab Email tutorial, so feedback from developers is welcome. What you'll end up with An agent that sends email from its own address (not your personal inbox) Replies arriving as structured data the agent can read Conversation threads as a first-class object Step 1 — Get a Secret Key Create an EngageLab account and generate a Secret Key from the console (it looks like sk_sg_xxx — the prefix encodes the region). Or use the CLI to create one via browser login: npm install -g @engagelabemail/cli engagelab-email-cli login You'll also need a mailbox — create one in the console (shared subdomain is fastest to start; custom domains need DNS verification). Step 2 — Register the MCP server For Claude Code: claude mcp add engagelab-email \ -e ENGAGELAB_EMAIL_SECRET_KEY=sk_sg_yourkey \ -- npx -y @engagelabemail/mcp Or in claude_desktop_config.json : { "mcpServers": { "engagelab-email": { "command": "npx", "args": ["-y", "@engagelabemail/mcp"], "env": { "ENGAGELAB_EMAIL_SECRET_KEY": "sk_sg_yourkey" } } } } Step 3 — Talk to it Ask your agent: List my mailboxes, then send an email from the first one to me@example.com saying "invoice #42 approved", then check for new messages. The agent now has 9 tools: send, reply, list inbound mail, get a message, poll for new mail, and browse threads. Why a dedicated mailbox (not Gmail access) Blast radius: the agent can only read/write its own mailbox Threads: replies group into conversations, so the agent keeps context Machine-first: everything is JSON over MCP — no IMAP parsing Gotchas Sandbox mode ( sandbox: true in send_email) skips real delivery while you're iterating on prompts Attachments are base64 in the tool schema — fine for do