MCP server MultiMail

@multimail/mcp-server

Your agent doesn't have email yet because nobody trusts it with email yet. MultiMail fixes that. A real email address with a trust ladder from read-only to fully autonomous, cryptographic identity on every message, and per-recipient sending controls.

Quick start

{
  "mcpServers": {
    "multimail": {
      "type": "url",
      "url": "https://mcp.multimail.dev/mcp"
    }
  }
}

Remote server. No install. Authenticates via OAuth on first connect.

Works with Claude.ai, Claude Desktop, Claude Code, Cursor, Windsurf, Copilot (VS Code), ChatGPT Desktop, and any MCP client that supports remote servers.

Alternative: local stdio server

{
  "mcpServers": {
    "multimail": {
      "command": "npx",
      "args": ["-y", "@multimail/mcp-server"],
      "env": {
        "MULTIMAIL_API_KEY": "mm_live_...",
        "MULTIMAIL_MAILBOX_ID": "01KJ1NHN8J..."
      }
    }
  }
}

Get a key at multimail.dev. Or run without one to create an account interactively.

Config file locations

Client	Config file
Claude Code	~/.claude/.mcp.json
Claude Desktop	claude_desktop_config.json
Cursor	.cursor/mcp.json in your project
Windsurf	~/.codeium/windsurf/mcp_config.json
Copilot (VS Code)	.vscode/mcp.json in your project
OpenCode	mcp.json in your project
ChatGPT Desktop	Settings > MCP Servers

Trust ladder

Every mailbox has an oversight mode. Start restrictive, graduate as the agent earns trust.

Mode	Behavior
read_only	Agent reads email. All sends blocked.
gated_all	Every action requires human approval.
gated_send	Outbound held for approval. Inbound immediate. (default)
monitored	Agent sends freely. Copies go to oversight address.
autonomous	Full send/receive. No gates.

Agents request upgrades via the API. The operator approves with a one-time code. Downgrades need no approval. The agent can always restrict itself.

The gated approval flow is formally verified in Lean 4. No email reaches delivery without passing through operator approval, for every possible code path.

Per-recipient allowlist

In gated_send mode, allowlisted recipients bypass the approval queue. Add exact addresses (vendor@example.com) or domain wildcards (*@example.com). Every addition requires operator email approval. The agent cannot self-approve allowlist changes.

The practical middle ground: routine correspondence with known contacts goes immediately, new recipients still require oversight.

Cryptographic identity

Every outbound email carries a signed X-MultiMail-Identity header (ECDSA P-256). The payload includes operator name, oversight mode, capabilities, and verification status. Recipients verify against the public key at GET /.well-known/multimail-signing-key.

A separate X-MultiMail-Reputation header links to privacy-preserving reputation data: bounce rates, complaint rates, account age. No raw addresses exposed.

Without verified identity, recipients cannot distinguish your agent from a spammer. With it, they can verify the operator, the oversight level, and the sending history before reading a word.

Agent DID relay (optional). If your agent has bound a did:key to its MultiMail account, pass an optional ucan parameter to send_email / reply_email. MultiMail relays your agent's self-signed UCAN verbatim in a separate X-Agent-Identity header (did="…"; ucan="…") — it does not sign or vouch for it; recipient tooling verifies the delegation independently. Inert unless a DID is bound.

Agent self-registration (auth.md)

Agents can register themselves without a browser. The protocol uses verified-email identity assertion, following the auth.md convention inspired by WorkOS AuthKit:

POST /agent/auth -> claim_token + OTP sent to operator email
POST /agent/auth/claim/complete -> API key + tenant_id + granted scopes

Discovery follows RFC 9728:

• GET /.well-known/oauth-protected-resource (resource metadata)
• GET /.well-known/oauth-authorization-server (authorization metadata with agent_auth extension)
• GET /auth.md (human/agent-readable registration guide)

The WWW-Authenticate header on 401 responses points agents to these endpoints automatically. An agent that hits a 401 can follow the link, read the registration protocol, and onboard itself.

Content scanning

Every outbound email is scanned before delivery. Emails enter pending_scan status, then transition to delivery or pending_send_approval (in gated modes). Inbound emails go through the same pipeline. Phishing, malware, and prompt injection patterns are flagged before reaching the agent's inbox.

How it works

• Email bodies are markdown in, formatted HTML out. Inbound HTML arrives as clean markdown (15x fewer tokens than raw MIME).
• Threading is automatic. Reply to an email and headers are set correctly.
• Sends return pending_scan while scanned. Gated mailboxes then transition to pending_send_approval for human review. Do not retry.
• Every outbound email carries a cryptographically signed X-MultiMail-Identity header.
• Reputation data via X-MultiMail-Reputation header: bounce rates, complaint rates, account age. Privacy-preserving, updated daily.

Tools (50)

Tool	Description
Core email
send_email	Send email as markdown. Supports attachments, idempotency_key, scheduled delivery via send_at.
check_inbox	List emails with filters: status, sender, subject, date range, direction, attachments, pagination.
read_email	Full email content. Trusted metadata and untrusted body returned as separate content blocks.
reply_email	Reply in-thread. Threading headers set automatically.
get_thread	All emails in a conversation thread with participants and metadata.
download_attachment	Download attachment as base64 with content type.
cancel_message	Cancel a pending or scheduled email.
edit_scheduled_email	Edit scheduled email before it sends.
wait_for_email	Block until matching email arrives or timeout (max 120s).
get_tags	Get all tags on an email. Persistent key-value agent memory across sessions.
set_tags	Set tags on an email. Merges with existing tags.
delete_tag	Delete a specific tag key from an email.
Oversight
list_pending	Emails awaiting oversight decision (requires oversight scope).
decide_email	Approve or reject a pending email (requires oversight scope).
manage_upgrade	Request or apply oversight mode upgrade (action: request|apply).
Sending allowlist
list_allowlist	List sending allowlist entries.
add_allowlist_entry	Add a recipient to the sending allowlist. Operator approval required.
remove_allowlist_entry	Remove an allowlist entry.
Mailbox management
list_mailboxes	All mailboxes with ID, address, oversight mode, display name.
configure_mailbox	First-run setup: oversight mode, display name, CC/BCC, scheduling, signature.
update_mailbox	Update settings (display name, oversight mode, signature, webhooks).
create_mailbox	Create mailbox (admin scope + operator approval).
delete_mailbox	Permanently delete a mailbox (admin scope).
Account & billing
get_account	Account status, plan, quota, sending enabled, enforcement tier.
update_account	Update org name, oversight email, physical address.
delete_account	Permanently delete account and all data (admin scope).
get_usage	Quota and usage stats for the billing period.
upgrade_plan	Upgrade to paid plan (Builder $9/mo, Pro $29/mo, Scale $99/mo).
cancel_subscription	Cancel paid subscription, revert to starter at period end.
get_billing_portal	Stripe portal URL for self-service billing.
Signup (no API key needed)
request_challenge	ALTCHA proof-of-work challenge for account creation.
create_account	Create account with solved PoW challenge.
resend_confirmation	Resend activation email with new code.
activate_account	Activate account using confirmation code.
setup_multimail	Guided onboarding on the public /onboard endpoint.
API keys & audit
list_api_keys	List all API keys (admin scope).
create_api_key	Create API key with scopes (admin + operator approval). send+oversight rejected to prevent self-approval.
revoke_api_key	Revoke an API key (admin scope).
get_audit_log	Account audit log (admin scope).
Contacts & spam
search_contacts	Search contacts by name or email.
add_contact	Add a contact.
delete_contact	Delete a contact.
manage_spam_status	Report spam or clear spam status (action: report|clear).
list_spam	Spam-flagged and quarantined emails.
list_suppression	List suppressed recipients with pagination.
remove_suppression	Remove a recipient from the suppression list.
Webhooks
create_webhook	Create webhook for real-time email event notifications.
list_webhooks	List all webhooks.
delete_webhook	Delete a webhook.
Meta
report_issue	Report a bug, site problem, or feature request.

Example prompts

Find the most recent email from alice@example.com, summarize what she's asking,
then draft a reply saying I'll review this week. Don't send until I approve.

Check my inbox and summarize the last 5 unread emails.
For each: sender, subject, time, and whether it needs action today.

Review the pending approval queue. For each pending email: who it goes to,
the subject, risk factors, and whether to approve or reject.

Show my current sending allowlist. Then add *@acme.com so emails to Acme skip approval.

Environment variables

Variable	Required	Description
MULTIMAIL_API_KEY	For stdio mode	Your API key (mm_live_...). Not needed for remote server (uses OAuth).
MULTIMAIL_MAILBOX_ID	No	Default mailbox ID. If unset, pass mailbox_id per tool or call list_mailboxes.
MULTIMAIL_API_URL	No	API base URL. Defaults to https://api.multimail.dev.

Also available

• REST API: https://api.multimail.dev (OpenAPI spec)
• CLI: npx -y @mvanhorn/printing-press install multimail (every API endpoint as a shell command)
• SDKs: Python, Vercel AI SDK, LangChain, LlamaIndex, CrewAI, AutoGen

Development

npm install
npm run dev   # Run with tsx
npm run build # Compile TypeScript
npm start     # Run compiled version

License

MIT

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