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An event machine based IMAP client
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An EventMachine based IMAP client.


gem install em-imap


This document tries to introduce concepts of IMAP alongside the facilities of the library that handle them, to give you an idea of how to perform basic IMAP operations. IMAP is more fully explained in RFC3501, and the details of the library are of course in the source code.


Before you can communicate with an IMAP server, you must first connect to it. There are three connection parameters, the hostname, the port number, and whether to use SSL/TLS. As with every method in EM::IMAP, EM::IMAP.connect returns a deferrable enhanced by the deferrable_gratification library.

For example, to connect to Gmail's IMAP server, you can use the following snippet:

require 'rubygems'
require 'em-imap'

EM::run do
  client = EM::IMAP.connect('', 993, true)
  client.errback do |error|
    puts "Connecting failed: #{error}"
  end.callback do |hello_response|
    puts "Connecting succeeded!"
  end.bothback do


There are two authentication mechanisms in IMAP, LOGIN and AUTHENTICATE, exposed as two methods on the EM::IMAP client, .login(username, password) and .authenticate(mechanism, *args). Again these methods both return deferrables, and the cleanest way to tie deferrables together is to use the .bind! method from deferrable_gratification.

Extending our previous example to also log in to Gmail:

client = EM::IMAP.connect('', 993, true)
client.bind! do
  client.login("", ENV["GMAIL_PASSWORD"])
end.callback do
  puts "Connected and logged in!"
end.errback do |error|
  puts "Connecting or logging in failed: #{error}"

The .authenticate method is more advanced and uses the same extensible mechanism as Net::IMAP. The two mechanisms supported by default are 'LOGIN' and 'CRAM-MD5', other mechanisms are provided by gems like gmail_xoauth.

Mailbox-level IMAP

Once the authentication has completed successfully, you can perform IMAP commands that don't require a currently selected mailbox. For example to get a list of the names of all Gmail mailboxes (including labels):

client = EM::IMAP.connect('', 993, true)
client.bind! do
  client.login("", ENV["GMAIL_PASSWORD"])
end.bind! do
end.callback do |list|
end.errback do |error|
  puts "Connecting, logging in or listing failed: #{error}"

The useful commands available to you at this point are .list, .create(mailbox), .delete(mailbox), .rename(old_mailbox, new_mailbox), .status(mailbox). .select(mailbox) and .examine(mailbox) are discussed in the next section, and .subscribe(mailbox), .unsubscribe(mailbox), .lsub and .append(mailbox, message, flags?, date_time) are unlikely to be useful to you immediately. For a full list of IMAP commands, and detailed considerations, please refer to RFC3501.

Message-level IMAP

In order to do useful things which actual messages, you need to first select a mailbox to interact with. There are two commands for doing this, .select(mailbox), and .examine(mailbox). They are the same except that .examine opens a mailbox in read-only mode; so that no changes are made (i.e. performing commands doesn't mark emails as read).

For example to search for all emails relevant to em-imap in Gmail:

client = EM::IMAP.connect('', 993, true)
client.bind! do
  client.login("", ENV["GMAIL_PASSWORD"])
end.bind! do'[Google Mail]/All Mail')
end.bind! do'ALL', 'SUBJECT', 'em-imap')
end.callback do |results|
  puts results
end.errback do |error|
  puts "Something failed: #{error}"

Once you have a list of message sequence numbers, as returned by search, you can actually read the emails with .fetch:

client = EM::IMAP.connect('', 993, true)
client.bind! do
  client.login("", ENV["GMAIL_PASSWORD"])
end.bind! do'[Google Mail]/All Mail')
end.bind! do'ALL', 'SUBJECT', 'em-imap')
end.bind! do |results|
  client.fetch(results, 'BODY[TEXT]')
end.callback do |emails|
  puts{|email| email.attr['BODY[TEXT]'] }
end.errback do |error|
  puts "Something failed: #{error}"

The useful commands available to you at this point are .search(*args), .expunge, .fetch(messages, attributes), .store(messages, name, values) and .copy(messages, mailbox). If you'd like to work with UIDs instead of sequence numbers, there are UID based alternatives: .uid_search, .uid_fetch, .uid_store and .uid_copy. The .close command and .check command are unlikely to be useful to you immediately.

Untagged responses

IMAP has the notion of untagged responses (aka. unsolicited responses). The idea is that sometimes when you run a command you'd like to be updated on the state of the mailbox with which you are interacting, even though notification isn't always required. To listen for these responses, the deferrables returned by each client method have a .listen(&block) method. All responses received by the server, up to and including the response that completes the current command will be passed to your block.

For example, we could insert a listener into the above example to find out some interesting numbers:

end.bind! do'[Google Mail]/All Mail').listen do |response|
    when "EXISTS"
      puts "There are #{} total emails in All Mail"
    when "RECENT"
      puts "There are #{} new emails in All Mail"
end.bind! do

One IMAP command that exists solely to receive such unsolicited responses is IDLE. The IDLE command blocks the connection so that no other commands can use it, so before you can send further commands you must stop the IDLE command:

idler = client.idle

idler.listen do |response|
  if ( == "EXISTS" rescue nil)
    puts "Ooh, new emails!"
    idler.callback do
      # ... process new emails
end.errback do |e|
  puts "Idler recieved an error: #{e}"


IMAP is an explicitly concurrent protocol: clients MAY send commands without waiting for the previous command to complete, and servers MAY send any untagged response at any time.

If you want to receive server responses at any time, you can call .add_response_handler(&block) on the client. This returns a deferrable like the IDLE command, on which you can call stop to stop receiving responses (which will cause the deferrable to succeed). You should also listen on the errback of this deferrable so that you know when the connection is closed:

handler = client.add_response_handler do |response|
  puts "Server says: #{response}"
end.errback do |e|
  puts "Connection closed?: #{e}"
end{ handler.stop }

If you want to send commands without waiting for previous replies, you can also do so. em-imap handles the few cases where this is not permitted (for example, during an IDLE command) by queueing the command until the connection becomes available again. If you do this, bear in mind that any blocks that are listening on the connection may receive responses from multiple commands interleaved.

client = EM::Imap.connect('', 993, true).callback do
  logger_in = client.login('', ENV["GMAIL_PASSWORD"])
  selecter ='[Google Mail]/All Mail')
  searcher ='').callback do |results|
    puts results

  logger_in.errback{ |e| e }
  selecter.errback{ |e| e }
  searcher.errback{ |e| "Something failed: #{e}" }


em-imap is still very much a work-in-progress, and the API will change as time goes by.

Before version 1, at least the following changes should be made:

  1. Stop using Net::IMAP in quite so many bizarre ways, probably clearer to copy-paste the code and rename relevant classes (particular NoResponseError..)
  2. Find a nicer API for some commands (maybe some objects to represent mailboxes, and/or messages?)
  3. Document argument serialization.
  4. Support SORT and THREAD.
  5. Put the in-line documentation into a real format.


Em-imap is made available under the MIT license, see LICENSE.MIT for details

Patches and pull-requests are welcome.

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