Email MCP Server for Claude Desktop
marginal is a hosted email MCP server you can wire into Claude Desktop in a couple of minutes. Once connected, Claude can generate subject line variants, launch real A/B tests, and read back open and click results — all through the Model Context Protocol.
Why use marginal with Claude Desktop
Claude Desktop supports MCP servers, which means you can give Claude access to live email marketing tools instead of just chatting about copy. With the marginal email MCP integration, Claude moves from drafting subject lines to actually testing them against your audience and reporting which one wins.
Because marginal is fully hosted, there's no local process to run and nothing to self-host. You point Claude Desktop at the https://marginal.sh/mcp endpoint, authenticate with a Bearer API key, and the four tools become available inside your conversations.
- Run a subject line A/B test from a natural-language prompt
- Generate multiple variants without leaving Claude Desktop
- Pull within-test lift metrics, opens, and clicks on demand
- Let Claude recommend the next experiment based on results
Add the marginal MCP server to Claude Desktop
Open your Claude Desktop configuration file and add marginal as a remote MCP server. Replace the placeholder with your own key, which starts with marg_live_. You can create a key from the marginal dashboard.
After saving the config, restart Claude Desktop so it picks up the new server. The marginal tools should appear in the MCP tool list for any new conversation.
- Endpoint: https://marginal.sh/mcp
- Registry name: sh.marginal/mcp
- Auth: Bearer API key (marg_live_...)
- Full setup notes: https://marginal.sh/docs/
What Claude can do once connected
The marginal email MCP server exposes four focused tools that map cleanly to an A/B testing workflow. Claude Desktop can chain them together in a single session: brainstorm variants, launch a managed send, wait for engagement to accumulate, then summarize the winner.
- generate_variants — produce candidate subject lines for a campaign
- launch_test — start a subject line A/B test with a managed send
- get_results — fetch open/click tracking and within-test lift
- recommend_next — suggest the next experiment to run
A practical first workflow
Try a single end-to-end loop to confirm everything works. Ask Claude something like: "Generate five subject line variants for our spring re-engagement email and launch an A/B test." Claude calls generate_variants and then launch_test, returning a test ID you can reference later.
Come back after the send has run and ask Claude for results. It will call get_results, report the lift between variants, and use recommend_next to propose your follow-up. This is AI agent email marketing in practice — the agent owns the experiment loop while you stay in the conversation.
- The free tier covers 100 experiments per month to get started
- Keep your marg_live_ key out of shared chat logs
- Reuse winning subject lines as a baseline for the next test
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