MCP Server for Email Marketing
marginal is a hosted MCP server for email marketing that gives your AI agent the tools to generate subject lines, run A/B tests, send campaigns, and read back lift metrics — all over the Model Context Protocol.
What an email MCP server does
An MCP server exposes a set of tools that AI agents can call directly. With marginal, the agent doesn't just draft copy — it can execute the full experiment loop without you leaving your editor or copy-pasting between dashboards.
marginal ships four tools focused on the parts of email marketing that benefit most from automation and measurement.
- generate_variants — produce subject line candidates to test
- launch_test — start a subject line A/B test with a managed send
- get_results — pull open/click tracking and within-test lift
- recommend_next — get a data-backed suggestion for the next variant or send
Running a subject line A/B test
The most common use case for an MCP server for email marketing is testing subject lines before a full send. With marginal, your AI agent can generate several variants, launch a split test, and then read open and click rates without manual setup.
Because the server tracks within-test lift, you get a clear read on which subject line outperformed rather than guessing from raw open counts. The agent can then call recommend_next to decide what to send to the remainder of your list.
- Ask your agent to draft and test 4–5 subject line variants
- marginal handles the managed send and split allocation
- Open and click tracking is reported back automatically
- Lift metrics make the winning variant unambiguous
AI agent email marketing in practice
marginal works with the MCP clients developers already use — Cursor, Claude Desktop, Claude Code, OpenAI Codex, Windsurf, Cline, Continue, and Zed. Point any of them at https://marginal.sh/mcp with a Bearer API key and the email marketing tools become available to the agent.
This makes AI agent email marketing a natural extension of an existing workflow: describe the campaign in plain language, and the agent calls generate_variants, launch_test, and get_results on your behalf.
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Registry: sh.marginal/mcp
Hosted, with a free tier to start
marginal is fully hosted — there's no self-hosted MCP server to deploy or maintain. You connect a compatible client, authenticate, and start running experiments.
The free tier includes 100 experiments per month, which is enough to validate the workflow on real campaigns before scaling up. Full tool reference and setup steps are in the docs at https://marginal.sh/docs/.
- Free tier: 100 experiments/month
- No infrastructure to run — marginal is hosted
- Docs: https://marginal.sh/docs/
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