UniOne

unione-mcp

The official Model Context Protocol server for UniOne (https://docs.unione.io). It lets AI assistants — Claude, ChatGPT, Cursor, Windsurf, VS Code, Cline and any other MCP client — work with your UniOne account: send email, manage sender domains, templates, webhooks, suppressions, event dumps, tags and projects. 32 tools, each one a call of the public UniOne Web API.

Two ways to use it:

• Remote — the hosted server at https://mcp.unione.io/mcp. Nothing to install: add the URL to your client and sign in to UniOne through OAuth.
• Local — the server runs on your machine over stdio (npx, Docker or a binary) and acts with the API key you put into UNIONE_API_KEY.

Remote server (OAuth)

URL: https://mcp.unione.io/mcp

The client opens the UniOne sign-in page on first use; you approve the access and the client keeps the token. Revoke it at any time in your UniOne account.

Claude Code

claude mcp add --transport http unione https://mcp.unione.io/mcp

Claude Desktop / claude.ai — Settings → Connectors → Add custom connector, URL https://mcp.unione.io/mcp.

Cursor, Windsurf, Cline, VS Code and other clients with an mcpServers config:

{
  "mcpServers": {
    "unione": {
      "type": "http",
      "url": "https://mcp.unione.io/mcp"
    }
  }
}

A client that cannot do OAuth can send an API key instead: add the header Authorization: Bearer <UniOne API key>.

Local server (API key)

Get an API key in your UniOne account: an account key reaches the whole account, a project key only its project. The server reads it from UNIONE_API_KEY.

npx (Node.js 18+; downloads the binary for your platform on first run):

{
  "mcpServers": {
    "unione": {
      "command": "npx",
      "args": ["-y", "unione-mcp"],
      "env": { "UNIONE_API_KEY": "<your API key>" }
    }
  }
}

Docker:

{
  "mcpServers": {
    "unione": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-e", "UNIONE_API_KEY", "ghcr.io/unione-repo/unione-mcp", "stdio"],
      "env": { "UNIONE_API_KEY": "<your API key>" }
    }
  }
}

Binary — download unione-mcp-<os>-<arch> from Releases, make it executable and put it on your PATH (or go install github.com/unione-repo/unione-mcp/cmd/unione-mcp@latest):

{
  "mcpServers": {
    "unione": {
      "command": "unione-mcp",
      "args": ["stdio"],
      "env": { "UNIONE_API_KEY": "<your API key>" }
    }
  }
}

Claude Code, in one line:

claude mcp add unione --env UNIONE_API_KEY=<your API key> -- npx -y unione-mcp

Check the connection by asking "show my UniOne account": the assistant calls get_account.

Tools

Every tool has a class, sent to the client as MCP annotations:

• read — reads only (readOnlyHint);
• write — creates or changes something, nothing is lost (destructiveHint: false);
• dangerous — deletes or overwrites for good, or cannot be taken back (destructiveHint: true). Clients ask you before such a call.

Area	Tool	What it does	Class
Account	get_account	Get UniOne account	read
Domains	list_domains	List sender domains	read
Domains	get_dns_records	Add domain / get its DNS records	write
Domains	validate_domain	Check domain DNS records	read
Domains	delete_domain	Delete sender domain	dangerous
Domains	get_sandbox_domain	Get sandbox domain	write
Confirmed emails	list_confirmed_emails	List confirmed emails	read
Confirmed emails	add_confirmed_email	Add confirmed email	write
Confirmed emails	delete_confirmed_email	Delete confirmed email	dangerous
Sending	send_email	Send email (billed)	dangerous
Templates	list_templates	List templates	read
Templates	get_template	Get template	read
Templates	set_template	Create or overwrite template	dangerous
Templates	delete_template	Delete template	dangerous
Webhooks	list_webhooks	List webhooks	read
Webhooks	get_webhook	Get webhook	read
Webhooks	set_webhook	Create or overwrite webhook	dangerous
Webhooks	delete_webhook	Delete webhook	dangerous
Suppressions	get_suppression	Get suppression of an address	read
Suppressions	list_suppressions	List suppressions	read
Suppressions	set_suppression	Block an address	dangerous
Suppressions	delete_suppression	Unblock an address	dangerous
Validation	validate_email	Validate an email address (billed)	write
Event dumps	request_event_dump	Request event dump	write
Event dumps	get_event_dump	Get event dump	read
Event dumps	delete_event_dump	Delete event dump	dangerous
Tags	list_tags	List tags	read
Tags	delete_tag	Delete tag	dangerous
Projects	list_projects	List projects	read
Projects	create_project	Create project	write
Projects	update_project	Update project	dangerous
Projects	delete_project	Delete project	dangerous

send_email sends real mail and cannot be recalled. validate_email is billed per address. The tools that reach beyond your account — send_email and add_confirmed_email mail an address, set_webhook points UniOne at a URL, validate_email probes a mailbox — say so with openWorldHint: true.

Read-only and no-send modes

Two switches narrow the tool list of a local server:

Variable	Effect
MCP_READ_ONLY=1	only the read tools are listed: the assistant cannot change the account
MCP_DISABLE_SEND=1	send_email is not listed: the assistant cannot send mail

"env": { "UNIONE_API_KEY": "<your API key>", "MCP_READ_ONLY": "1" }

With Docker, env reaches only the docker process: pass the switch into the container with its own -e, before the image name.

"args": ["run", "-i", "--rm", "-e", "UNIONE_API_KEY", "-e", "MCP_READ_ONLY", "ghcr.io/unione-repo/unione-mcp", "stdio"],
"env": { "UNIONE_API_KEY": "<your API key>", "MCP_READ_ONLY": "1" }

They guard against mistakes of the model, not against the key's owner: the same key works in the Web API directly. For a hard limit use a project API key.

Configuration

Everything is an environment variable; a .env file in the working directory is read too. .env.example lists them all. Every value is validated at start-up.

Variable	Purpose
UNIONE_API_KEY	local mode: the API key every tool acts with
UNIONE_API_URL	Web API base, default https://api.unione.io/en/transactional/api/v1
MCP_TRANSPORT	http (default) or stdio; unione-mcp stdio sets it too
MCP_READ_ONLY, MCP_DISABLE_SEND	see above
AUTH_MODE	self-hosted http mode: api_key (default) or oauth
AUTHORIZATION_SERVER_URL, OAUTH_SCOPES, OAUTH_TOKEN_PREFIX, MCP_PUBLIC_URL	self-hosted oauth mode. OAUTH_TOKEN_PREFIX defaults to uoat_.
LISTEN_HOST, PORT	self-hosted http mode listener (default: every interface, first free port from 3000)
UPSTREAM_TIMEOUT, UPSTREAM_MAX_BODY_BYTES, MCP_MAX_REQUEST_BYTES	Web API call limits and the /mcp body cap
LOG_LEVEL, LOG_FORMAT	debug, info, warn, error; text or json, always to stderr

The API key, the Authorization header and Web API response bodies are never logged.

Documentation

• UniOne API: https://docs.unione.io
• Installing with an AI agent: llms-install.md
• Reporting a vulnerability: SECURITY.md
• Issues and pull requests: CONTRIBUTING.md

Development

go build -o bin/unione-mcp ./cmd/unione-mcp
go test ./internal/... ./cmd/...                     # unit tests, no network

# acceptance: the real binary over HTTP and stdio against a WireMock stand-in of the API
docker run -d --rm -p 8081:8081 wiremock/wiremock:3.4.1 --local-response-templating --port 8081
E2E_WIREMOCK_URL=http://localhost:8081 go test -tags=integration ./tests/...

License

MIT