What is Mailbuttons (mbag.ai)?

Governed email for AI agents (Mailbuttons / mbag.ai): sandbox inboxes, policy gate, audit log.

How do I install Mailbuttons (mbag.ai)?

Clone Mailbuttons (mbag.ai) from https://github.com/mailbuttons/mcp-server and configure it as an MCP server in your client (Claude Desktop, Cursor, or VS Code).

Is Mailbuttons (mbag.ai) open source?

Yes, Mailbuttons (mbag.ai) is open source under the MIT license. Source code is available at https://github.com/mailbuttons/mcp-server.

What category does Mailbuttons (mbag.ai) belong to?

Mailbuttons (mbag.ai) is listed under Communication MCP servers on MCPFind.

Mailbuttons (mbag.ai) — MCP Server for Communication

Mailbuttons MCP server

Governed email for AI agents, over the Model Context Protocol. Give an agent a scoped mailbox where the server enforces the guardrails, not the prompt: sandbox-by-default inboxes, a policy gate on every send, and a tamper-evident audit log. External sending and scope changes are human-approved, never granted by the agent itself.

Registry: com.mailbuttons/mcp-server
npm: @mailbuttons/mcp-server
Platform: mailbuttons.com · agent front door: mbag.ai

Use it

Hosted (recommended) — a streamable-HTTP endpoint served by the platform:

https://mailbuttons.com/api/v1/mcp/rpc
Authorization: Bearer <your Mailbuttons MCP token>   # mb_sandbox_... (or mb_prod_...)

Local (stdio) — run the npm package and let your agent launch it:

{
  "mcpServers": {
    "mailbuttons": {
      "command": "npx",
      "args": ["-y", "@mailbuttons/mcp-server"],
      "env": { "MAILBUTTONS_API_KEY": "mb_sandbox_..." }
    }
  }
}

Get a scoped token from the dashboard or POST /api/v1/mcp/sandbox-inboxes. Sandbox tokens can never send externally until a human promotes them.

What the server enforces

Inbound — a per-mailbox sender policy, fail-closed: mail from strangers bounces by default, so nobody can prompt-inject your agent just by emailing it.
Outbound — a recipient blocklist the agent can read but not change; a blocked send returns a normal {"status":"blocked"} result, not an error.
Caps + audit — per-account send caps and a hash-chained audit log that records refusals too.
Escalation — sending externally or widening scope is propose-only; a named human approves. The agent cannot approve its own request.

Install as an agent skill

This repo ships a root SKILL.md, so any skills-aware agent can add it:

npx skills add mailbuttons/mcp-server

Docs

Agent signup (for agents): https://mbag.ai/docs/agent-signup.md
Trust model: https://mbag.ai/docs/trust-model.md
OpenAPI: https://mbag.ai/api/openapi.json
Framework recipes: references/ (Claude Agent SDK, LangChain, plain SDK)

Mailbuttons is a trading name of Code Cutter Limited (UK, no. 08453060). MIT licensed.

Set up in your AI client

AI clientOperating system

Merge this template into ~/Library/Application Support/Claude/claude_desktop_config.json. Keep existing servers. Add any arguments, credentials, and permissions required by the maintainer; this template has not been install-tested.

json

{
  "mcpServers": {
    "com-mailbuttons-mcp-server": {
      "command": "npx",
      "args": [
        "-y",
        "@mailbuttons/mcp-server"
      ]
    }
  }
}

Restart Claude Desktop completely for changes to take effect. Confirm the server appears connected in the client’s tool list, then try a read-only example from its documentation.

Claude Desktop setup reference

Compatible MCP Clients

Mailbuttons (mbag.ai) works with any MCP-compatible client. Copy the config snippet from the Configuration section above and add it to the file shown for your client, then restart the application.

Claude Desktop~/Library/Application Support/Claude/claude_desktop_config.jsonRestart Claude Desktop completely for changes to take effect.

Cursor~/.cursor/mcp.jsonRestart Cursor for changes to take effect.

VS Code.vscode/mcp.jsonReload VS Code window for changes to take effect.

Windsurf~/.codeium/windsurf/mcp_config.jsonRestart Windsurf for changes to take effect.

Claude Code.mcp.jsonSave at the project root, then start Claude Code in that project and review the MCP server approval prompt. Keep real credentials out of shared files.

Mailbuttons (mbag.ai)