Net::IMAP

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality. The protocol is described in [IMAP].

IMAP Overview

An IMAP client connects to a server, and then authenticates itself using either #authenticate() or #login(). Having authenticated itself, there is a range of commands available to it. Most work with mailboxes, which may be arranged in an hierarchical namespace, and each of which contains zero or more messages. How this is implemented on the server is implementation-dependent; on a UNIX server, it will frequently be implemented as a files in mailbox format within a hierarchy of directories.

To work on the messages within a mailbox, the client must first select that mailbox, using either #select() or (for read-only access) #examine(). Once the client has successfully selected a mailbox, they enter selected state, and that mailbox becomes the current mailbox, on which mail-item related commands implicitly operate.

Messages have two sorts of identifiers: message sequence numbers, and UIDs.

Message sequence numbers number messages within a mail box from 1 up to the number of items in the mail box. If new message arrives during a session, it receives a sequence number equal to the new size of the mail box. If messages are expunged from the mailbox, remaining messages have their sequence numbers “shuffled down” to fill the gaps.

UIDs, on the other hand, are permanently guaranteed not to identify another message within the same mailbox, even if the existing message is deleted. UIDs are required to be assigned in ascending (but not necessarily sequential) order within a mailbox; this means that if a non-IMAP client rearranges the order of mailitems within a mailbox, the UIDs have to be reassigned. An IMAP client cannot thus rearrange message orders.

Examples of Usage

List sender and subject of all recent messages in the default mailbox

imap = Net::IMAP.new('mail.example.com')
imap.authenticate('LOGIN', 'joe_user', 'joes_password')
imap.examine('INBOX')
imap.search(["RECENT"]).each do |message_id|
  envelope = imap.fetch(message_id, "ENVELOPE")[0].attr["ENVELOPE"]
  puts "#{envelope.from[0].name}: \t#{envelope.subject}"
end

Move all messages from April 2003 from “Mail/sent-mail” to “Mail/sent-apr03”

imap = Net::IMAP.new('mail.example.com')
imap.authenticate('LOGIN', 'joe_user', 'joes_password')
imap.select('Mail/sent-mail')
if not imap.list('Mail/', 'sent-apr03')
  imap.create('Mail/sent-apr03')
end
imap.search(["BEFORE", "30-Apr-2003", "SINCE", "1-Apr-2003"]).each do |message_id|
  imap.copy(message_id, "Mail/sent-apr03")
  imap.store(message_id, "+FLAGS", [:Deleted])
end
imap.expunge

Thread Safety

Net::IMAP supports concurrent threads. For example,

imap = Net::IMAP.new("imap.foo.net", "imap2")
imap.authenticate("cram-md5", "bar", "password")
imap.select("inbox")
fetch_thread = Thread.start { imap.fetch(1..-1, "UID") }
search_result = imap.search(["BODY", "hello"])
fetch_result = fetch_thread.value
imap.disconnect

This script invokes the FETCH command and the SEARCH command concurrently.

Errors

An IMAP server can send three different types of responses to indicate failure:

instance, the username/password used for logging in are incorrect;
the selected mailbox does not exists; etc.

understanding of the IMAP protocol.  This includes attempting
commands from the wrong client state; for instance, attempting
to perform a SEARCH command without having SELECTed a current
mailbox.  It can also signal an internal server
failure (such as a disk crash) has occurred.

logout sequence, and can be used as part of a login sequence
to indicate that the server is (for some reason) unwilling
to accept our connection.  As a response to any other command,
it indicates either that the server is shutting down, or that
the server is timing out the client connection due to inactivity.

These three error response are represented by the errors Net::IMAP::NoResponseError, Net::IMAP::BadResponseError, and Net::IMAP::ByeResponseError, all of which are subclasses of Net::IMAP::ResponseError. Essentially, all methods that involve sending a request to the server can generate one of these errors. Only the most pertinent instances have been documented below.

Because the IMAP class uses Sockets for communication, its methods are also susceptible to the various errors that can occur when working with sockets. These are generally represented as Errno errors. For instance, any method that involves sending a request to the server and/or receiving a response from it could raise an Errno::EPIPE error if the network connection unexpectedly goes down. See the socket(7), ip(7), tcp(7), socket(2), connect(2), and associated man pages.

Finally, a Net::IMAP::DataFormatError is thrown if low-level data is found to be in an incorrect format (for instance, when converting between UTF-8 and UTF-16), and Net::IMAP::ResponseParseError is thrown if a server response is non-parseable.

References

[IMAP]

1. Crispin, “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1”,

RFC 2060, December 1996. (Note: since obsoleted by RFC 3501)

[LANGUAGE-TAGS]

Alvestrand, H., “Tags for the Identification of Languages”, RFC 1766, March 1995.

[MD5]

Myers, J., and M. Rose, “The Content-MD5 Header Field”, RFC 1864, October 1995.

[MIME-IMB]

Freed, N., and N. Borenstein, “MIME (Multipurpose Internet Mail Extensions) Part One: Format of Internet Message Bodies”, RFC 2045, November 1996.

[RFC-822]

Crocker, D., “Standard for the Format of ARPA Internet Text Messages”, STD 11, RFC 822, University of Delaware, August 1982.

[RFC-2087]

Myers, J., “IMAP4 QUOTA extension”, RFC 2087, January 1997.

[RFC-2086]

Myers, J., “IMAP4 ACL extension”, RFC 2086, January 1997.

[RFC-2195]

Klensin, J., Catoe, R., and Krumviede, P., “IMAP/POP AUTHorize Extension for Simple Challenge/Response”, RFC 2195, September 1997.

[SORT-THREAD-EXT]

Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - SORT and THREAD Extensions”, draft-ietf-imapext-sort, May 2003.

[OSSL]

http://www.openssl.org

[RSSL]

http://savannah.gnu.org/projects/rubypki

[UTF7]

Goldsmith, D. and Davis, M., “UTF-7: A Mail-Safe Transformation Format of Unicode”, RFC 2152, May 1997.