marginal.sh Signup and Email MCP Quickstart
Searching for how the marginal.sh signup flow works with email MCP? This guide walks through creating an account, getting your API key, and pointing an AI agent at the hosted email MCP server so it can run subject line tests on your behalf.
What you get after marginal.sh signup
marginal is a hosted email MCP server built for AI agents. Once you complete signup, you receive a Bearer API key in the form marg_live_... that authenticates every request to the endpoint at https://marginal.sh/mcp. There is nothing to deploy or self-host — the server runs on our side and your agent simply calls it.
The free tier includes 100 experiments per month, which is enough to validate the workflow before scaling up.
- API key auth via Bearer token (marg_live_...)
- Registry name: sh.marginal/mcp
- Endpoint: https://marginal.sh/mcp
- 100 experiments/month on the free tier
The MCP tools your agent can call
After signup, your AI agent gains access to four MCP tools. Together they cover the full loop of an email subject line A/B test: drafting variants, sending them, measuring engagement, and deciding what to do next.
- generate_variants — produce candidate subject lines to test
- launch_test — run a subject line A/B test with managed sends
- get_results — pull open/click tracking and within-test lift metrics
- recommend_next — get a data-backed suggestion for the next step
Connecting an AI agent to the email MCP server
marginal works as a standard MCP server, so any compatible client can use it for AI agent email marketing. Supported clients include Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed.
Configuration is the same across clients: add the marginal.sh signup email MCP endpoint and pass your Bearer key. Your agent then orchestrates a subject line A/B test end to end — generating variants, launching the send, and reading the lift numbers without you wiring up an ESP by hand.
A typical first experiment
Once connected, ask your agent to draft three subject lines for an upcoming campaign and launch a test. marginal handles the managed send and tracking; get_results returns within-test lift so you can see which line earned more opens and clicks. Then recommend_next tells you whether to scale the winner or keep iterating.
Full setup steps and tool schemas are documented at https://marginal.sh/docs/.
- Generate variants from a campaign brief
- Launch the subject line A/B test
- Read open/click and lift metrics
- Act on the recommended next step
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