Finding an Email Server in the MCP Registry
If you're searching the MCP registry for an email server your AI agent can call, marginal is a hosted option built specifically for subject line testing and managed sends. Here's how it's published, what tools it exposes, and how to wire it up.
What 'MCP registry email server' means
The Model Context Protocol lets AI agents discover and call external tools through a standard interface. A registry entry is simply a published identifier that tells a client where the server lives and what it does. marginal is registered as sh.marginal/mcp and runs as a hosted email MCP server — there's nothing to self-host or deploy.
Unlike a generic transactional email gateway, marginal focuses on experimentation: it generates subject line variants, launches A/B tests, sends through a managed pipeline, and reports lift. Your agent reasons over the results and picks a winner.
- Registry name: sh.marginal/mcp
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Hosted — no local server process to run
Tools the server exposes
Once connected, your agent sees four tools that cover a complete subject line A/B test loop. They're designed to be chained: generate options, launch the test, read the data, then decide what to do next.
- generate_variants — produce candidate subject lines for a campaign
- launch_test — start a managed A/B test across your audience
- get_results — pull open/click tracking and within-test lift metrics
- recommend_next — get a data-backed suggestion for the next send
Why use a hosted email MCP server for testing
Running a subject line A/B test by hand means setting up segments, sending variants, and crunching open and click rates before you can act. A hosted email MCP server collapses that into agent-callable steps, so AI agent email marketing workflows can run end to end without leaving your editor or assistant.
Because marginal handles the sends and tracking, you don't manage separate provider keys inside the protocol layer. The agent calls a tool, the server runs the experiment, and you get lift numbers back.
- Subject line A/B test from a single tool call
- Open and click tracking handled server-side
- Within-test lift metrics for confident decisions
- Free tier: 100 experiments per month
Connecting from your MCP client
marginal works with the common MCP clients, so you can call it from whichever tool your team already uses. Point the client at the endpoint, add your Bearer key, and the four tools appear automatically.
Supported clients include Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed. Full setup steps live in the docs at https://marginal.sh/docs/, and the endpoint reference is at https://marginal.sh/mcp.
- Add the https://marginal.sh/mcp endpoint to your client config
- Authenticate with your marg_live_ API key
- Start with generate_variants, then launch_test
- Read get_results and let recommend_next guide the next send
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