The Hosted MCP Email Server for AI Agents
If you searched for a hosted MCP email server, you want subject line testing and managed sends that plug straight into your AI agent — without standing up infrastructure. That's exactly what marginal does.
What a hosted MCP email server gives you
marginal is a fully hosted email MCP server. You point your agent at a single endpoint, authenticate with a Bearer API key, and the email marketing tools are available immediately. There is no container to run, no queue to babysit, and no self-hosted MCP server to patch.
Because the server is hosted, sends, tracking, and metrics all run on marginal's side. Your agent just calls tools and reads results.
- Endpoint: https://marginal.sh/mcp
- Auth: Bearer API key (marg_live_...)
- Registry identifier: sh.marginal/mcp
- No self-hosted option to maintain — it's hosted for you
Run a subject line A/B test from your agent
The core workflow is a subject line A/B test driven by AI agent email marketing. Generate candidate subject lines, launch a managed test, then read open and click metrics with within-test lift so the agent knows which variant won.
Each tool maps to one step of the loop, so an agent can iterate without you stitching together separate APIs.
- generate_variants — draft subject line candidates
- launch_test — start a managed A/B send
- get_results — pull open/click and lift metrics
- recommend_next — decide the follow-up action
Built for agent clients you already use
marginal works with the MCP clients developers and growth engineers reach for daily. Connect once and the email MCP server tools show up alongside your other agent capabilities.
Supported clients include Cursor, OpenAI Codex, Claude Desktop, Claude Code, Windsurf, Cline, Continue, and Zed. Setup details live in the docs at https://marginal.sh/docs/.
Start testing on the free tier
You can validate the entire hosted MCP email server flow on the free tier, which includes 100 experiments per month. That's enough to wire up an agent, run several subject line A/B tests, and confirm the lift metrics before scaling up.
Grab an API key, set the endpoint to https://marginal.sh/mcp, and let your agent take it from there.
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