Email MCP Quickstart with marginal
This email MCP quickstart walks you from zero to a live subject line A/B test in minutes. marginal is a hosted email marketing MCP server, so there's nothing to deploy — point your agent at the endpoint, drop in your API key, and start running experiments.
What you need before you start
marginal exposes a single hosted endpoint at https://marginal.sh/mcp. Authentication uses a Bearer API key in the form marg_live_..., which you generate from your account. Because the email MCP server is fully managed, you don't run any local process or provision an SMTP backend yourself.
- An MCP-capable client (Cursor, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Zed, or OpenAI Codex)
- A marginal API key (marg_live_...)
- The endpoint URL: https://marginal.sh/mcp
- The free tier covers 100 experiments/month — enough to learn the workflow
The four tools you'll use
Once connected, your AI agent has access to four MCP tools that map cleanly to the lifecycle of an experiment. You can drive the whole flow conversationally, or wire it into an automated AI agent email marketing pipeline.
- generate_variants — produce candidate subject lines from a brief or campaign goal
- launch_test — kick off a subject line A/B test with a managed send
- get_results — pull open and click tracking plus within-test lift metrics
- recommend_next — let the agent suggest the next move based on results
Running your first subject line A/B test
A typical email MCP quickstart loop looks like this: ask your agent to draft a handful of subject lines, launch a test against a segment, then check back once enough opens have accumulated. marginal handles the send, the split, and the tracking, returning lift metrics scoped to that specific test so you can compare variants fairly.
Keep your first test small and clear. Pick one variable — the subject line — and let recommend_next guide whether to roll out a winner or iterate. This is where the AI agent email marketing workflow earns its keep, since the agent can reason over results instead of you eyeballing a dashboard.
Where to go next
After your first run, read the docs at https://marginal.sh/docs/ for tool schemas, segment options, and details on how within-test lift is calculated. From there you can layer marginal into larger agent workflows — drafting, testing, and promoting subject lines without leaving your editor.
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