The MCP Server Email Send Tool for AI Agents
If you're searching for an MCP server email send tool that your AI agent can call directly, marginal handles the full loop: generate variants, send the test, and read the results — all through standard MCP tools.
What the send tool actually does
marginal is a hosted email MCP server, so the send step isn't a raw SMTP call you wire up yourself. Instead, your agent invokes the launch_test tool, which dispatches the campaign through marginal's managed sending infrastructure and begins tracking opens and clicks immediately.
That means the 'email send tool' part of the workflow is one MCP call, not a stack of delivery config. Your agent decides what to send; marginal delivers it and records performance.
- generate_variants — produce subject line and copy options
- launch_test — run the managed send for a subject line A/B test
- get_results — pull open/click and within-test lift metrics
- recommend_next — get the suggested winner or next step
Why route sends through an email MCP server
Letting an AI agent fire off emails through ad-hoc scripts gets messy fast — no consistent tracking, no structured results to reason over. An email MCP server gives the agent a typed contract: it knows exactly what arguments launch_test expects and what shape get_results returns.
For AI agent email marketing, that structure is the whole point. The agent can chain a subject line A/B test, wait for engagement data, and act on the recommendation without a human stitching the steps together.
- Consistent open and click tracking on every managed send
- Within-test lift metrics so the agent compares variants fairly
- A single Bearer API key (marg_live_...) instead of per-step credentials
Connecting your client
marginal works with the MCP clients developers already use — Cursor, Claude Desktop, Claude Code, OpenAI Codex, Windsurf, Cline, Continue, and Zed. Point your client at the endpoint https://marginal.sh/mcp and authenticate with your API key.
Once connected, the send tool and the rest of the toolset appear to your agent automatically. Find setup details and tool schemas at https://marginal.sh/mcp and the docs at https://marginal.sh/docs/.
- Endpoint: https://marginal.sh/mcp
- Registry: sh.marginal/mcp
- Auth: Bearer API key (marg_live_...)
- Free tier: 100 experiments per month
A typical send-and-measure loop
The fastest path to value: ask your agent to draft variants, launch the test, and report back. Because marginal is hosted, there's no self-hosted MCP server to maintain — the send tool and tracking run on marginal's side.
- Call generate_variants to get competing subject lines
- Call launch_test to send the subject line A/B test
- Poll get_results for opens, clicks, and lift
- Call recommend_next to confirm the winner before a broader send
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