EngageLab Agent Email MCP Server is EngageLab's official email project, distributed as a local stdio MCP server. It does not provide hosted OAuth or HTTP MCP endpoints and must be run locally via an installation command. It lets AI agents send, receive, and reply to emails through the Model Context Protocol.
Purpose: Each agent is assigned an independent mailbox (a real address that can send and receive), and conversations are grouped by thread so the agent has the full historical context. It is suitable for scenarios requiring email conversations, such as customer service, scheduling, and approvals.
Main capabilities:
- Sending and receiving: Agents have a dedicated mailbox rather than an external parsing webhook.
- Thread awareness: Replies are automatically grouped into the same conversation, and the agent can see the full history.
- Sandbox mode: Test agent workflows without sending emails to real users.
- Single environment variable: No OAuth is required for local use, and the region is automatically inferred from the key prefix.
How to use:
- Get a Secret Key: Create an EngageLab account and generate a key in the console (format sk_sg_xxx; the prefix determines the region); or use the CLI: engagelab-email-cli login to create one through the browser.
- Create a mailbox: Create a mailbox for the agent in the console (the shared subdomain is available immediately; custom domains require DNS verification). Programmatic mailbox creation is on the roadmap. If list_mailboxes returns empty, it means the account does not yet have a mailbox.
- Register the server: Add a configuration block to Claude Desktop's claude_desktop_config.json. Installation command (build the MCPB package): The generated package is located at dist/engagelab-agent-email.mcpb and can be uploaded via Smithery publishing. The server is also listed in the official MCP Registry, with the server name io.github.Metaverse-Cloud/engagelab-email and the npm package @engagelabemail/mcp.
Applicable scenarios: Compatible with Claude Desktop, Claude Code, Cursor, Cowork, and any MCP-compatible client. A typical loop is, for example, a customer service bot.
Limitations: A maximum of 10 attachments per message, 10MB total (base64-encoded in the tool schema).
Troubleshooting:
- list_mailboxes returns an empty list: The account has no mailbox and one must be created in the console (agents cannot yet provision mailboxes on their own).
- 401 / code 100101: The Secret Key is incorrect or has been revoked. Check whether ENGAGELAB_EMAIL_SECRET_KEY and the region prefix (sk_sg_ / sk_tr_) match the endpoint being used.
- Unable to determine the API base URL: The key's region prefix is unrecognized, so ENGAGELAB_EMAIL_BASE_URL must be set explicitly.
- Replies appear as new conversations: Use reply_email (not send_email) to preserve the In-Reply-To header and threading.
Roadmap: Hosted MCP (OAuth) for zero-configuration remote use; programmatic mailbox creation via Secret Key; webhook push (no polling required) for check_new_messages; URL-based attachment references (no need to use base64 in context).
Other: It can be run from source; the EngageLab Agent Email CLI provides terminal operations for the same mailbox, with --json output for easy use by agents; the EngageLab Node SDK / Python SDK can send emails from code.
