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"I'M A Proxy" - Node.js IMAP proxy server

This is a simple proxy server to monitor and modify IMAP communications.

Individual plugins can subscribe to certain IMAP commands sent by either the client or the server and intercept or alter the exchanged data.

The primary use-case is to hide non-mail folders of a Kolab server by filtering LSUB/LIST/XLIST responses.

Warning: this is only a proof-of-concept application and neither fully tested nor reviewed for security issues. DON'T USE IT IN A PRODUCTIVE ENVIRONMENT!

Installation

  • Download and install node.js with npm.
  • Clone this git repository
  • Copy the config.js.dist into config.js and adjust the config
  • Run the proxy with node imaproxy.js [<path-to-config-file>]

Features

  • Asynchronous, non-blocking socket connections
  • TLS/SSL support for both client and server connections
  • Full IMAP payload logging
  • Easily extensible with plugins

Available Plugins

  • mailonly.js

    Modifies LSUB/LIST/XLIST responses to hide non-mail folders from being listed to the clients. The folder type is determined by fetching /vendor/kolab/folder-type annotations from the IMAP server.

  • zlogger.js

    Writes full IMAP payload to console.log() if enabled by the imap_log config option.

TODOs

  • Configurable logging output (maybe a plugin?)
  • Spawn and manage multiple processes using the cluser module
  • STARTTLS support for client connections
  • COMPRESS=DEFLATE support for client connections
  • Test with different IMAP clients
    • Thunderbird ✓
    • Apple Mail ✓
    • iOS Mail ✓
    • Microsoft Outlook
    • Sparrow Mac
    • Sparrow iOS
    • Android Mail
    • Android K9
  • Stress testing

Troubleshooting

For every client connection, the imaproxy needs to keep two socket connections open. You may therefore hit the limit of max. file descriptors per process. Increase ulimit -n accordingly.

Further file descriptors are used when the proxy opens a new connection to the server and has to resolve the host name. This can be avoided and speeded up by configuring the IMAP server with its IP address instead of the host name.

Install as a Daemon

There are many ways how to daemonize node.js applications. Here's one approach using pm2:

Install pm2 globally:

$ npm install pm2 -g

Start a pm2 process using the configuration file:

$ pm2 start imaproxy.js -- /opt/imaproxy/config.js --name imaproxy

Use pm2 --help to see possible actions to monitor running node.js processes.

In order to automatically run the imap proxy on startup, let pm2 register a startup script for your platform:

$ pm2 startup
$ pm2 save

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see www.gnu.org/licenses/.