Email MCP Server Documentation
Looking for clear email MCP server documentation? This page walks through how marginal exposes email marketing as MCP tools so AI agents can generate variants, launch sends, and read back lift metrics without leaving your editor.
What the marginal email MCP server does
marginal is a hosted email MCP server. Instead of running infrastructure yourself, you point an MCP-capable agent at the endpoint and authenticate with a Bearer API key. The agent then gets a focused set of tools for AI agent email marketing — no scripting against raw send APIs required.
The server is built specifically around subject line A/B testing and managed sends, so the tool surface stays small and predictable. That makes it easy for an agent to reason about what comes next in an experiment.
- Endpoint: https://marginal.sh/mcp
- Registry name: sh.marginal/mcp
- Auth: Bearer API key in the form marg_live_...
- Hosted only — there is no self-hosted MCP server to deploy
The four MCP tools
Everything in the email MCP server documentation revolves around four tools. They map directly to the lifecycle of a subject line A/B test, from drafting candidates to acting on results.
- generate_variants — produce candidate subject lines for a campaign
- launch_test — start a managed send that splits traffic across variants
- get_results — pull open/click tracking and within-test lift metrics
- recommend_next — get a data-backed suggestion for the next move
How an agent runs a subject line A/B test
A typical flow strings the tools together. The agent calls generate_variants to draft options, launch_test to send them, and then polls get_results as opens and clicks accumulate. Because lift is measured within the test, the agent can compare variants on equal footing before calling recommend_next.
This keeps the human in the loop where it matters — you review variants and approve the launch — while the agent handles the mechanical steps of measuring and reporting.
- Draft subject lines with generate_variants
- Approve and launch with launch_test
- Track open and click performance via get_results
- Let recommend_next surface the winning direction
Supported clients and getting started
The marginal email MCP server works with the common MCP clients, so you can drive subject line A/B tests from the tools you already use: Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed.
The free tier includes 100 experiments per month, which is enough to validate the workflow before scaling. Full reference material lives in the docs, and the connection endpoint is the same one used throughout this guide.
- Connect any supported MCP client to https://marginal.sh/mcp
- Free tier: 100 experiments per month
- Full docs: https://marginal.sh/docs/
- MCP endpoint: https://marginal.sh/mcp
Get started with marginal
marginal is a hosted email marketing MCP server at marginal.sh. Sign up free, create an API key, and connect https://marginal.sh/mcp from Cursor, Codex, or Claude Desktop.
- 100 experiments/month on the free tier
- Four MCP tools: generate_variants, launch_test, get_results, recommend_next
- Listed in the MCP Registry as sh.marginal/mcp