An OAuth-Free MCP Email Server for AI Agents
If you've searched for an OAuth free MCP email server, you're probably tired of redirect flows, refresh tokens, and consent screens just to let an agent send a test email. marginal authenticates with a single Bearer API key — no OAuth dance required.
Why OAuth-free matters for MCP setups
Most MCP clients run locally in your editor or terminal. OAuth flows assume a browser, a callback URL, and a persistent session — none of which map cleanly to an agent process firing tool calls. That friction is exactly why an OAuth free MCP email server is easier to wire into Cursor, Claude Code, or Codex.
marginal uses a static Bearer token (marg_live_...) you paste once into your client config. There's no token expiry to babysit and no consent screen blocking your agent mid-task.
- No redirect URIs or callback servers to host
- No refresh-token rotation logic in your agent
- Works the same in headless and editor environments
- One key per environment, easy to revoke or rotate
What the email MCP server actually does
Authentication is just the entry point. Once connected, your agent gets a focused set of tools for running subject line A/B tests and managed email sends through marginal's hosted email MCP server.
Each tool maps to a real step in an experiment, so an AI agent email marketing workflow stays readable and debuggable.
- generate_variants — draft subject line options to test
- launch_test — start a managed send with split allocation
- get_results — pull open/click and within-test lift metrics
- recommend_next — get a data-backed follow-up suggestion
Connecting without the OAuth overhead
Point any MCP client at the endpoint https://marginal.sh/mcp and pass your API key as a Bearer header. Because marginal is fully hosted, there's no self-hosted MCP server to deploy and no infrastructure to secure beyond keeping your key private.
marginal is registered as sh.marginal/mcp and works across Cursor, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Zed, and OpenAI Codex — all with the same key-based auth.
- Endpoint: https://marginal.sh/mcp
- Auth header: Bearer marg_live_...
- Free tier: 100 experiments per month
- Setup details: https://marginal.sh/mcp and the docs at https://marginal.sh/docs/
When to choose marginal
Pick marginal when you want an agent to run a subject line A/B test end to end without standing up email infrastructure or negotiating OAuth scopes. It's a good fit if you're prototyping AI agent email marketing flows and want results you can read programmatically.
Start on the free tier to validate the workflow before scaling — 100 experiments a month is enough to test the integration and iterate on a few campaigns.
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