When your agent runs stripe projects add, ship it MultiMail instead of a generic SMTP provider. Verifiable sender identity and oversight gating come standard.
Stripe launched Projects.dev in March 2026, a CLI that lets agents and developers provision third-party services directly from the terminal. Launch partners cover analytics (PostHog), hosting (Vercel, Railway), databases (Supabase, Neon, PlanetScale, Turso, Chroma), auth (Clerk), and email. The same 48-hour window saw companion CLI launches from Ramp, Sendblue, ElevenLabs, Visa, Resend, and Google Workspace — the broader “everything is CLI” convergence Latent Space documented.
MultiMail is the agent-governed email option for stacks bootstrapped through Projects.dev. Generic email providers solve transactional throughput; MultiMail adds the layer agents actually need: oversight modes that gate sends before delivery, ECDSA-signed sender identity that survives the agent context, and an MCP server the coding agent already knows how to call.
The mental model: Stripe's Shared Payment Tokens identify the agent at the billing layer; MultiMail's X-MultiMail-Identity header identifies the agent at the messaging layer. Together they cover the two main surfaces an agent acts through.
MultiMail exposes a provisioning shape compatible with the Agentic Provisioning Protocol pattern Projects.dev uses. The MCP setup_multimail tool returns the same kind of structured config the agent expects from any partner.
Every outbound email carries a cryptographically signed identity header. The sender remains verifiable long after the agent session ends — so audit, compliance, and downstream systems can independently check who sent what.
Five oversight modes from read_only through autonomous. Coding agents typically start in gated_send (every email approved before delivery) and graduate as trust builds — the trust ladder built into the API.
Claude Code, Cursor, Windsurf, and Zed all support MCP. One config line at mcp.multimail.dev gives the agent 41 email tools — no SDK install, no credential juggling, no per-CLI auth flow.
"cm"># Illustrative — partner manifest entry the agent would resolve
stripe projects add multimail/email \
--plan builder \
--domain agent.example.com
"cm"># Stripe handles billing, MultiMail provisions the mailbox.
"cm""># The CLI returns a scoped API key into the project env:
"cm"># MULTIMAIL_API_KEY=mm_live_...
"cm"># MULTIMAIL_MAILBOX_ID=mb_...MultiMail is not yet a Projects.dev launch partner — the manifest entry above shows the shape the integration would take. Today, run stripe projects init and add MultiMail credentials manually as project env vars; the rest of the flow is identical.
import os, requests
"cm"># Stripe Projects.dev injects these env vars into the project
API_KEY = os.environ["MULTIMAIL_API_KEY"]
MAILBOX = os.environ["MULTIMAIL_MAILBOX_ID"]
"cm"># Mailbox is configured in gated_send mode —
"cm""># every send queues for approval before delivery
resp = requests.post(
"https://api.multimail.dev/v1/send",
headers={"Authorization": f"Bearer {API_KEY}"},
json={
"mailbox_id": MAILBOX,
"to": "[email protected]",
"subject": "Your MRR is up 12% this week",
"body": "Hey — quick weekly update from the agent..."
}
)
print(resp.json()) "cm"># {"status": "pending_approval", "message_id": "msg_..."}The MultiMail API key arrives as a project env var alongside Stripe's other partner credentials.
{
"mcpServers": {
"multimail": {
"type": "sse",
"url": "https://mcp.multimail.dev/mcp",
"headers": {
"Authorization": "Bearer ${MULTIMAIL_API_KEY}"
}
}
}
}Drop into ~/.cursor/mcp.json, ~/.claude/mcp.json, or your editor's equivalent. The agent picks up all 41 email tools on next restart.
Sign up at multimail.dev and verify your sending domain. Generate an API key — it will start with mm_live_.
Run stripe projects init in your repo. This creates a project that aggregates billing across partner services.
Add MULTIMAIL_API_KEY and MULTIMAIL_MAILBOX_ID as project env vars. The coding agent will see them on next session start, alongside whatever Vercel, Supabase, or Clerk keys Projects.dev injected.
Drop the MCP config snippet above into your editor. The agent now has 41 email tools available without writing any SDK code.
While the agent is new to your stack, leave the mailbox in gated_send mode. Approve emails through the MultiMail dashboard. Promote to monitored or autonomous once the agent has demonstrated correct behavior.
stripe projects add posthog/analytics and Projects.dev creates an account on the partner service, returns an API key, and sets up unified billing — without touching the partner's signup flow. Launch partners include Vercel, Railway, Supabase, Neon, PlanetScale, Turso, Chroma, PostHog, Clerk, and others.Email infrastructure built for AI agents. Verifiable identity, graduated oversight, and a 38-tool MCP server. Formally verified in Lean 4.