Claws Mail MCP Plugin

What claws-mail-mcp-plugin MCP server does

The claws-mail-mcp-plugin MCP server adds an MCP interface to a running Claws Mail desktop client. Rather than connecting directly to a mail provider, it exposes the accounts and mail data already configured in Claws Mail. An MCP-capable AI application can use that interface to inspect folders and messages, search mail, change folder and message flags, and perform common message actions.

Supported operations include composing new messages, replying, forwarding, sending, and receiving mail. The plugin also provides a status tool and a plugin_version tool, according to the project’s build and version documentation. A read-only mode can be enabled through configuration when message-changing or sending operations should not be available.

How it works

The plugin is loaded by Claws Mail and runs in the same process as the mail client. It starts a local HTTP service on 127.0.0.1; MCP requests use JSON-RPC and the endpoint is protected with a bearer token. Because the service binds to the loopback address, an AI client must run on the same computer as Claws Mail.

On each start, the plugin writes a client configuration file named mcp_client.json into the Claws Mail configuration directory. That file contains the active endpoint URL and token, allowing the values to be copied into an MCP client configuration. The registry entry is intended for discovery only because the registry does not accept loopback URLs as remote connection endpoints.

Setup and configuration

Prebuilt plugin files are available for supported Claws Mail and operating-system combinations. Install the matching binary in the directory reported by pkg-config --variable=plugindir claws-mail, restart Claws Mail, and enable the plugin under Configuration > Plugins if it does not load automatically.

The claws-mail-mcp-plugin MCP server reads its endpoint, port, bearer token, and read-only setting from mcp_pluginrc in the Claws Mail configuration directory. The generated mcp_client.json provides the resulting connection details. Claude Desktop must be configured locally; its custom connector flow uses Anthropic’s servers and cannot reach a loopback endpoint.

Building from source requires Meson, Ninja, a C compiler, Claws Mail development files, GTK3, GLib, GnuTLS, libgcrypt, and enchant. Linux and Windows MSYS2 build instructions use the same Meson configuration and compilation commands.

Tools and capabilities

The claws-mail-mcp-plugin MCP server supports:

• Reading folders and messages
• Searching mail
• Composing, replying to, and forwarding messages
• Sending and receiving mail through configured accounts
• Creating or managing folders and message flags
• Reporting plugin status and compiled version
• Restricting operation to read-only mode through configuration

The exact available actions depend on the running Claws Mail instance, its configured accounts, and whether read-only mode is enabled.

Limitations and notes

This is a local integration, not a hosted mail service. Only processes on the same machine can reach the endpoint, and Claws Mail must be running with the plugin loaded. The bearer token should be treated as a secret when copied into client configuration.

Prebuilt binaries are tied to supported Claws Mail versions and operating systems, with separate release artifacts for each tested combination. Source builds require the matching Claws Mail development environment. The project is licensed under GPL-3.0-or-later.