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    0.6.0 • Public • Published


    Imapper is an IMAP Server. It is descended directly from Hoodiecrow. However, Hoodiecrow is intended expicitly as a test server, not for production use. It only supports in-memory message storage, single user, no external authentication, and many other limitations. In the words of the talented Andris Reiman, it is intended only for testing.

    Imapper builds on hoodiecrow to turn it into the first usable, pluggable, production-quality IMAP server written entirely in nodejs.

    Pluggable components include:

    • User database: list of users can be from config file, memory, active directory, LDAP, database, or anywhere.
    • Message store: The actual message storage can be in memory (ephemeral), on local disk, in NFS, an object store, or anywhere. It can be stored in any format, if a plugin exists to support it.

    Imapper offers IMAP4ver1 support.


    Run as a standalone server

    To run Imapper you need Node.js on your machine. Node should work on almost any platform, so Imapper should too.

    If you have Node.js installed, install Imapper with the npm command and run it:

    npm install -g imapper
    sudo imapper

    Sudo is needed to bind to port 143 (default for IMAP) or 993 (default for IMAP over SSL). If you choose to use a higher port, say 1143 (imapper -p 1143), you do not need to use sudo.

    imapper command also provides an incoming SMTP server which distributes all incoming messages appropriately. To use it, use smtpPort option (imapper --smtpPort=1025). The SMTP server has no proper filtering, security and scaling. You should not use the SMTP server in any production environment. If you need a production quality SMTP server in nodejs, check out Haraka.

    Protip Running imapper --help displays useful information about command line options for Imapper and some sample configuration data.

    After you have started Imapper server, you can point your IMAP client to <hostname>:143. Use the correct username and password as configured.

    Note that the storage driver for imapper as a standalone server is the memory storage. All data will be lost after shutting down the server.


    The Imapper command-line supports several options. Each can be passed as an environment variable, set as a command-line argument, or left to the default. Command-line overrides environment variable overrides default.

    • --port port or IMAP_PORT=port: which port to listen on. Default is 993 if --secure (SSL) or 143 if not.
    • --smtpPort or IMAP_SMTPPORT=port: which port to listen for SMTP delivered messages for testing only. Default is not to listen on SMTP.
    • --ssl true or IMAP_SSL=true: whether to listen over SSL on port 993 instead of clear on 143. Default is false.
    • --debug true or IMAP_DEBUG=true: whether to enable debug messages to console. Default is false.
    • --storage path or IMAP_STORAGE=path: path to a JSON file with the folders and messages to load on startup. Default is none.
    • --plugin plugin --plugin plugin ... or IMAP_PLUGINS=plugina,pluginb,...,pluginn: list of plugins to enable.
    • --config path or IMAP_CONFIG=path: path to a json file with config options suited to the imapper as a module. Default is none.

    Include as a Node.js module

    Add imapper dependency

    npm install --save imapper

    Create and start an IMAP server

    var imapper = require("imapper"),
        server = imapper(options);

    See complete.js for an example.


    Imapper requires configuration to tell it how to work.

    Providing Configuration

    The configuration is provided either as a JSON config file or a configuration object, depending on how Imapper is launched. In both ways, the structure of the configuration is identical and is described below.


    When launched from the command-line, Imapper requires a JSON configuration file. The path to the config file should be provided. If not, it will look for a file named imapper.json in the current directory from which imapper was launched.

    If no config file is provided, and imapper.json is not available in the current directory, Imapper will exit with an error.


    When Imapper is included as a module inside a nodejs program, you should not provide a configuration file. Instead, you should provide the JSON structure that would be in that config file as the options parameter.

    Essentially, launching imapper --config=/some/file.json from the command-line is equivalent to:

    var imapper = require("imapper"),
      config = require('/some/file.json'),
      server = imapper(config);

    Configuration Structure

    The configuration object or file contains information on how to configure, launch and run Imapper.

        tls: true,
        ssl: true,
        users: authModule,
        storage: storageModule

    Each key in the configuration represents a configurable element of Imapper.

    • tls: Whether to support upgradable TLS connections. Optional. Defaults to false. Relevant only if option ssl is not true.
    • ssl: Whether to run in SSL or clear mode. Optional. Defaults to false.
    • users: Plugin to use for user authentication. Required. See below.
    • storage: Plugin to use for message and folder storage. Required. See below.

    Each section of configuration that represents a plugin is a function that is returned by an appropriate plugin. You are expected to require() and configure the plugin appropriately.

    For example:

    var storagePlugin = require('imapper-file-storage')({basedir: '/var/spool/mail'}), imapper = require('imapper'),
    server = imapper({
        storage: storagePlugin

    Available Plugins

    The following plugins are available in npm as of this writing. By convention, all imapper plugins should be named according to imapper-type-name`.


    A simple plugin that stores all mail messages in memory. Terminating the server means they are lost.

    This plugin supports reading its initial data from a file or object. In the config object, provide one of the following:

    • data: The actual data to load
    • file: A JSON file containing the data to load.

    Note that this plugin replicates the behaviour of the original hoodiecrow.

    var storage = require('imapper-storage-memory')({
    // you now can pass storage to imapper
    server = require('imapper')({
        storage: storage


    Read usernames for authentication from an htpasswd file.

    Provide the path to the htpasswd file in the config as the option file.

    var users = require('imapper-users-htpasswd')({
        file: '/path/to/htpasswd'
    // you now can pass storage to imapper
    server = require('imapper')({
        users: users


    Include users directly in the configuration.

    In the config, each key is a username, while each value is a Bcrypt encrypted password.

    var users = require('imapper-users-static')({
        john: 'dasabsb657223asasa',
        jill: 'sasaswqwdbsb657223'
    // you now can pass storage to imapper
    server = require('imapper')({
        users: users

    Writing Plugins

    To write a plugin, you must follow the conventions for each type of plugin. Look in the directory plugins/ for a README for each type of plugin and a sample.



    All commands are supported but might be a bit buggy

    Supported Plugins

    Plugins can be enabled when starting the server but can not be unloaded or loaded when the server is already running. All plugins are self contained and not tied to core. If you do not enable a plugin, no trace of it is left to the system. For example, if you do not enable CONDSTORE, messages do not have a MODSEQ value set.

    • AUTH-PLAIN Adds AUTH=PLAIN capability. Supports SASL-IR [RFC4959] as well
    • CONDSTORE Partially implemented CONDSTORE [RFC4551] support
    • CREATE-SPECIAL-USE Enables CREATE-SPECIAL-USE [RFC6154] capability. Allowed special flags can be set with server option "special-use"
    • ENABLE Adds ENABLE capability [RFC5161]. Must be loaded before any plugin that requires ENABLE support (eg. CONDSTORE)
    • ID Adds ID [RFC2971] capability
    • IDLE Adds IDLE [RFC2177] capability
    • LITERALPLUS Enables LITERAL+ [RFC2088] capability
    • LOGINDISABLED Disables LOGIN support for unencrypted connections
    • NAMESPACE Adds NAMESPACE [RFC2342] capability
    • SASL-IR Enables SASL-IR [RFC4959] capability
    • SPECIAL-USE Enables SPECIAL-USE [RFC6154] capability Mailboxes need to have a "special-use" property (String or Array) that will be used as extra flag for LIST and LSUB responses
    • STARTTLS Adds STARTTLS command
    • UNSELECT Adds UNSELECT [RFC3691] capability
    • X-GM-EXT-1 Adds partial support for Gmail specific options. X-GM-MSGID is fully supported, X-GM-LABELS is partially supported (labels can be STOREd and FETCHed but setting a label does not change message behavior, for example the message does not get copied to another mailbox). X-GM-THRID is not supported as I haven't figured threading out yet.
    • XOAUTH2 GMail XOAUTH2 login. Only works with SALS-IR, if you need non SASL-IR support as well, let me know. Use "testuser" as the username and "testtoken" as Access Token to log in.
    • XTOYBIRD Custom plugin to allow programmatic control of the server. Login not required to use XTOYBIRD commands

    Planned but not yet implemented

    • MOVE
    • QUOTA

    Existing XTOYBIRD commands

    To use these functions, XTOYBIRD plugin needs to be enabled

    Available commands:

    • XTOYBIRD SERVER dumps server internals
    • XTOYBIRD CONNECTION dumps connection internals
    • XTOYBIRD STORAGE dumps storage as JSON
    • XTOYBIRD USERADD "username" "password" adds or updates user
    • XTOYBIRD USERDEL "username" removes an user
    • XTOYBIRD SHUTDOWN Closes the server after the last client disconnects. New connections are rejected.

    Example usage for XTOYBIRD STORAGE:

    S: * imapper ready for rumble
    S: * XTOYBIRD [XJSONDUMP] {3224}
    S: {
    S:     "INBOX": {
    S:         "messages": [
    S:             {
    S:                 "raw": "Subject: hello 1\r\n\r\nWorld 1!",
    S:                 ...
    S: A1 OK XTOYBIRD Completed

    Known issues

    • INBOX* as a separate namespace and managing INBOX subfolders is a mess. CREATE seems to work, DELETE is buggy and RENAME doesn't work with INBOX subfolders (unless the default namespace is "INBOX.", not ""). I need to rethink how this works.

    Not sure if these should be fixed or not

    • STORE does not emit notifications to other clients
    • MODSEQ updates are not notified

    These issues are probably not going to get fixed

    • Session flags are not supported (this means that \Recent flag is also not supported)
    • addr-adl (at-domain-list) values are not supported, NIL is always used
    • anonymous namespaces are not supported
    • STORE returns NO and nothing is updated if there are pending EXPUNGE messages
    • CHARSET argument is ignored

    Running tests

    Running tests requires you to have grunt-cli installed

    npm install -g grunt-cli

    After which you can run



    npm test

    Example configs




    Creating custom plugins

    A plugin can be a string as a pointer to a built in plugin or a function. Plugin function is run when the server is created and gets server instance object as an argument.

        // Add two plugins, built in "IDLE" and custom function
        plugin: ["IDLE", myAwesomePlugin]
    // Plugin handler
    function myAwesomePlugin(server){
        // Add a string to the capability listing
         * Add a new command XSUM
         * If client runs this command, the response is a sum of all
         * numeric arguments provided
         * A1 XSUM 1 2 3 4 5
         * * XSUM 15
         * A1 OK SUM completed
         * @param {Object} connection - Session instance
         * @param {Object} parsed - Input from the client in structured form
         * @param {String} data - Input command as a binary string
         * @param {Function} callback - callback function to run
        server.setCommandHandler("XSUM", function(connection, parsed, data, callback){
            // Send untagged XSUM response
                tag: "*",
                command: "XSUM",
                    [].concat(parsed.attributes || []).reduce(function(prev, cur){
                        return prev + Number(cur.value);
                    }, 0)
            }, "XSUM", parsed, data);
            // Send tagged OK response
                tag: parsed.tag,
                command: "OK",
                    // TEXT allows to send unquoted
                    {type: "TEXT", value: "XSUM completed"}
            }, "XSUM", parsed, data);

    Plugin mehtods

    Add a capability

    server.registerCapability(name[, availabilty])


    • name a string displayed in the capability response
    • availability a function which returns boolean value. Executed before displaying the capability response. If the function returns true, the capability is displayed, if false then not.


    // Display in CAPABILITY only in Not Authenticated state
    server.registerCapability("XAUTH", function(connection){
        return connection.state == "Not Authenticated";

    Define a command

    server.setCommandHandler(name, handler)


    • name is the command name
    • handler (connection, parsed, data, callback) is the handler function for the command

    Handler arguments

    • connection - Session instance
    • parsed - Input from the client in structured form (see imap-handler for reference)
    • data - Input command as a binary string
    • callback - callback function to run (does not take any arguments)

    The command should send data to the client with connection.send()

    connection.send(response, description, parsed, data, /* any additional data */)


    • response is a imap-handler compatible object. To get the correct tag for responsing OK, NO or BAD, look into parsed.tag
    • description is a string identifying the response to be used by other plugins
    • parsed is the parsed argument passed to the handler
    • data is the data argument passed to the handler
    • additional arguments can be used to provide input for other plugins

    Retrieve an existing handler

    To override existing commands you should first cache the existing command, so you can use it in your own command handler.

    server.getCommandHandler(name) -> Function


    • name is the function name


    var list = server.getCommandHandler("LIST");
    server.setCommandHandler("LIST", function(connection, parsed, data, callback){
        // do something
        console.log("Received LIST request");
        // run the cached command
        list(connection, parsed, data, callback);

    Reroute input from the client

    If your plugin needs to get direct input from the client, you can reroute the incoming data by defining a connection.inputHandler function. The function gets input data as complete lines (without the linebreaks). Once you want to reroute the input back to the command handler, just clear the function.

    connection.inputHandler = function(line){
        connection.inputHandler = false;

    See idle.js for an example

    Override output

    Any response sent to the client can be overriden or cancelled by other handlers. You should append your handler to server.outputHandlers array. If something is being sent to the client, the response object is passed through all handlers in this array.

    server.outputHandlers.push(function(connection, /* arguments from connection.send */){})

    response arguments from connection.send is an object and thus any modifications will be passed on. If skipResponse property is added to the response object, the data is not sent to the client.

    // All untagged responses are ignored and not passed to the client
    server.outputHandlers.push(function(connection, response, description){
        if(response.tag == "*"){
            response.skipResponse = true;
            console.log("Ignoring untagged response for %s", description);

    Other possbile operations

    It is possible to append messages to a mailbox; create, delete and rename mailboxes; change authentication state and so on through the server and connection methods and properties. See existing command handlers and plugins for examples.


    Imapper has debug levels that dump output. As of this writing, the only supported debug level is 1, which writes all received IMAP commands and sent IMAP responses, as well as errors, to the console. Each message is preceded by the unique connection ID - allowing you to filter the output sanely when multiple connections are in use - as well as R for received by imapper, S for sent by imapper, and E for error.

    Sample output:

    123 S: imapper ready to rumble
    123 R: A1 Capability
    123 S: A1 AUTH-PLAIN
    123 S: A1 OK
    123 R: A2 LOGIN abc def
    123 S: A2 OK

    All of the above are from the unique connection ID 123, and show which messages were sent by imapper or received by it.





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