Email Marketing Without SMTP Setup
Configuring an SMTP relay, warming IPs, and wiring up bounce handling is a project unto itself. marginal lets you skip all of it — it's a hosted email MCP server that handles delivery, tracking, and experiment logic so your AI agent can run real campaigns from day one.
Why SMTP setup is the part you can skip
Traditional email marketing means standing up an SMTP server or relay, managing authentication records, and building your own click and open tracking. That's a lot of plumbing before you send a single message.
With marginal, sending is managed for you. You connect over MCP, call a tool, and the message goes out with tracking already attached. There's no SMTP host, port, or credential to configure — and nothing to self-host.
- No SMTP server, relay, or port configuration
- Managed sends with open and click tracking built in
- Hosted endpoint at https://marginal.sh/mcp — no infrastructure to run
- Free tier covers 100 experiments/month to start
How AI agent email marketing works with marginal
marginal exposes a small set of MCP tools that map cleanly to the campaign lifecycle. An AI agent generates copy, launches a test, reads results, and decides what to do next — all through structured tool calls instead of manual dashboard work.
Because it's an MCP server, the same workflow runs inside whatever client you already use for coding and agent tasks: Cursor, Claude Desktop, Claude Code, Windsurf, Cline, Continue, Zed, and OpenAI Codex.
- generate_variants — draft subject line and copy options
- launch_test — send a managed A/B test, no SMTP required
- get_results — pull open, click, and within-test lift metrics
- recommend_next — get a data-backed suggestion for the next send
Running a subject line A/B test
The most direct payoff of skipping SMTP setup is how fast you can test. Ask your agent to generate a few subject line variants, launch them as a single A/B test, and let marginal split delivery and measure performance for you.
Lift is reported within the test itself, so you're comparing variants on a like-for-like audience rather than guessing across separate sends. When results land, recommend_next turns them into a clear path forward.
- Compare multiple subject lines in one managed test
- Within-test lift metrics keep comparisons honest
- Iterate in natural language from your MCP client
- Authenticate with a Bearer API key (marg_live_...)
Getting connected
Point your MCP client at the hosted endpoint and authenticate with your API key — that's the entire setup. There's no mail server to provision and no ESP API key juggling required to start running tests.
Full tool references and examples live in the docs at https://marginal.sh/docs/, including the exact arguments for generate_variants, launch_test, get_results, and recommend_next.
- Endpoint: https://marginal.sh/mcp
- Registry: sh.marginal/mcp
- Auth: Bearer API key
- Docs: https://marginal.sh/docs/
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