Remote MCP Email Server for Subject Line Testing
A remote MCP email server lets your AI agent run email experiments over a hosted endpoint — no infrastructure to maintain. marginal exposes subject line A/B testing, managed sends, and result tracking through the Model Context Protocol.
What a remote MCP email server does
Unlike a local tool you run yourself, a remote MCP email server is hosted and reachable over HTTPS. Your agent connects to a single endpoint and gets a stable set of tools — there's no daemon to install, no port to forward, and no version to keep patched.
marginal is that hosted email MCP server. It listens at https://marginal.sh/mcp and authenticates each request with a Bearer API key, so your agent can plan and run experiments from wherever it runs.
- Hosted endpoint: https://marginal.sh/mcp
- Auth via Bearer API key (marg_live_...)
- No self-hosted server to operate or scale
- Registry identifier: sh.marginal/mcp
Tools your agent gets
The server surfaces a focused set of MCP tools built around the subject line A/B test workflow. An AI agent can move from drafting variants to launching a test to reading results without leaving the conversation.
- generate_variants — draft candidate subject lines to test
- launch_test — start a managed send with the variants split across recipients
- get_results — pull open/click tracking and within-test lift metrics
- recommend_next — get a data-backed suggestion for the next experiment
Why remote fits AI agent email marketing
AI agent email marketing works best when the agent owns the full loop: hypothesize, send, measure, iterate. A remote MCP email server keeps that loop running on infrastructure that handles delivery and tracking, so the agent focuses on decisions rather than plumbing.
Because lift is measured within each test, your agent gets a clean read on which subject line actually won — useful context for the next round of generate_variants.
- Managed sends with open and click tracking included
- Within-test lift metrics for honest comparisons
- Free tier covers 100 experiments per month
- Iterate continuously with recommend_next
Connecting your MCP client
marginal works with the MCP clients developers already use — Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed. Point any of them at the remote endpoint, add your API key, and the four tools become available to the agent.
See the setup docs at https://marginal.sh/docs/ for per-client configuration details and the endpoint reference at https://marginal.sh/mcp.
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