21.15. "imaplib" --- IMAP4 protocol client
******************************************

**Source code:** Lib/imaplib.py

======================================================================

This module defines three classes, "IMAP4", "IMAP4_SSL" and
"IMAP4_stream", which encapsulate a connection to an IMAP4 server and
implement a large subset of the IMAP4rev1 client protocol as defined
in **RFC 2060**. It is backward compatible with IMAP4 (**RFC 1730**)
servers, but note that the "STATUS" command is not supported in IMAP4.

Three classes are provided by the "imaplib" module, "IMAP4" is the
base class:

class imaplib.IMAP4(host='', port=IMAP4_PORT)

   This class implements the actual IMAP4 protocol.  The connection is
   created and protocol version (IMAP4 or IMAP4rev1) is determined
   when the instance is initialized. If *host* is not specified, "''"
   (the local host) is used. If *port* is omitted, the standard IMAP4
   port (143) is used.

   The "IMAP4" class supports the "with" statement.  When used like
   this, the IMAP4 "LOGOUT" command is issued automatically when the
   "with" statement exits.  E.g.:

      >>> from imaplib import IMAP4
      >>> with IMAP4("domain.org") as M:
      ...     M.noop()
      ...
      ('OK', [b'Nothing Accomplished. d25if65hy903weo.87'])

   在 3.5 版更改: 支持了 "with" 语句。

Three exceptions are defined as attributes of the "IMAP4" class:

exception IMAP4.error

   Exception raised on any errors.  The reason for the exception is
   passed to the constructor as a string.

exception IMAP4.abort

   IMAP4 server errors cause this exception to be raised.  This is a
   sub-class of "IMAP4.error".  Note that closing the instance and
   instantiating a new one will usually allow recovery from this
   exception.

exception IMAP4.readonly

   This exception is raised when a writable mailbox has its status
   changed by the server.  This is a sub-class of "IMAP4.error".  Some
   other client now has write permission, and the mailbox will need to
   be re-opened to re-obtain write permission.

There's also a subclass for secure connections:

class imaplib.IMAP4_SSL(host='', port=IMAP4_SSL_PORT, keyfile=None, certfile=None, ssl_context=None)

   This is a subclass derived from "IMAP4" that connects over an SSL
   encrypted socket (to use this class you need a socket module that
   was compiled with SSL support).  If *host* is not specified, "''"
   (the local host) is used. If *port* is omitted, the standard IMAP4
   -over-SSL port (993) is used. *ssl_context* is a "ssl.SSLContext"
   object which allows bundling SSL configuration options,
   certificates and private keys into a single (potentially long-
   lived) structure.  Please read Security considerations for best
   practices.

   *keyfile* and *certfile* are a legacy alternative to *ssl_context*
   - they can point to PEM-formatted private key and certificate chain
   files for the SSL connection.  Note that the *keyfile*/*certfile*
   parameters are mutually exclusive with *ssl_context*, a
   "ValueError" is raised if *keyfile*/*certfile* is provided along
   with *ssl_context*.

   在 3.3 版更改: *ssl_context* parameter added.

   在 3.4 版更改: The class now supports hostname check with
   "ssl.SSLContext.check_hostname" and *Server Name Indication* (see
   "ssl.HAS_SNI").

   3.6 版后已移除: *keyfile* and *certfile* are deprecated in favor of
   *ssl_context*. Please use "ssl.SSLContext.load_cert_chain()"
   instead, or let "ssl.create_default_context()" select the system's
   trusted CA certificates for you.

The second subclass allows for connections created by a child process:

class imaplib.IMAP4_stream(command)

   This is a subclass derived from "IMAP4" that connects to the
   "stdin/stdout" file descriptors created by passing *command* to
   "subprocess.Popen()".

The following utility functions are defined:

imaplib.Internaldate2tuple(datestr)

   Parse an IMAP4 "INTERNALDATE" string and return corresponding local
   time.  The return value is a "time.struct_time" tuple or "None" if
   the string has wrong format.

imaplib.Int2AP(num)

   Converts an integer into a string representation using characters
   from the set ["A" .. "P"].

imaplib.ParseFlags(flagstr)

   Converts an IMAP4 "FLAGS" response to a tuple of individual flags.

imaplib.Time2Internaldate(date_time)

   Convert *date_time* to an IMAP4 "INTERNALDATE" representation. The
   return value is a string in the form: ""DD-Mmm-YYYY HH:MM:SS
   +HHMM"" (including double-quotes).  The *date_time* argument can be
   a number (int or float) representing seconds since epoch (as
   returned by "time.time()"), a 9-tuple representing local time an
   instance of "time.struct_time" (as returned by "time.localtime()"),
   an aware instance of "datetime.datetime", or a double-quoted
   string.  In the last case, it is assumed to already be in the
   correct format.

Note that IMAP4 message numbers change as the mailbox changes; in
particular, after an "EXPUNGE" command performs deletions the
remaining messages are renumbered. So it is highly advisable to use
UIDs instead, with the UID command.

At the end of the module, there is a test section that contains a more
extensive example of usage.

参见: Documents describing the protocol, and sources and binaries
  for servers implementing it, can all be found at the University of
  Washington's *IMAP Information Center*
  (https://www.washington.edu/imap/).


21.15.1. IMAP4 Objects
======================

All IMAP4rev1 commands are represented by methods of the same name,
either upper-case or lower-case.

All arguments to commands are converted to strings, except for
"AUTHENTICATE", and the last argument to "APPEND" which is passed as
an IMAP4 literal.  If necessary (the string contains IMAP4 protocol-
sensitive characters and isn't enclosed with either parentheses or
double quotes) each string is quoted. However, the *password* argument
to the "LOGIN" command is always quoted. If you want to avoid having
an argument string quoted (eg: the *flags* argument to "STORE") then
enclose the string in parentheses (eg: "r'(\Deleted)'").

Each command returns a tuple: "(type, [data, ...])" where *type* is
usually "'OK'" or "'NO'", and *data* is either the text from the
command response, or mandated results from the command. Each *data* is
either a string, or a tuple. If a tuple, then the first part is the
header of the response, and the second part contains the data (ie:
'literal' value).

The *message_set* options to commands below is a string specifying one
or more messages to be acted upon.  It may be a simple message number
("'1'"), a range of message numbers ("'2:4'"), or a group of non-
contiguous ranges separated by commas ("'1:3,6:9'").  A range can
contain an asterisk to indicate an infinite upper bound ("'3:*'").

An "IMAP4" instance has the following methods:

IMAP4.append(mailbox, flags, date_time, message)

   Append *message* to named mailbox.

IMAP4.authenticate(mechanism, authobject)

   Authenticate command --- requires response processing.

   *mechanism* specifies which authentication mechanism is to be used
   - it should appear in the instance variable "capabilities" in the
   form "AUTH=mechanism".

   *authobject* must be a callable object:

      data = authobject(response)

   It will be called to process server continuation responses; the
   *response* argument it is passed will be "bytes".  It should return
   "bytes" *data* that will be base64 encoded and sent to the server.
   It should return "None" if the client abort response "*" should be
   sent instead.

   在 3.5 版更改: string usernames and passwords are now encoded to
   "utf-8" instead of being limited to ASCII.

IMAP4.check()

   Checkpoint mailbox on server.

IMAP4.close()

   Close currently selected mailbox. Deleted messages are removed from
   writable mailbox. This is the recommended command before "LOGOUT".

IMAP4.copy(message_set, new_mailbox)

   Copy *message_set* messages onto end of *new_mailbox*.

IMAP4.create(mailbox)

   Create new mailbox named *mailbox*.

IMAP4.delete(mailbox)

   Delete old mailbox named *mailbox*.

IMAP4.deleteacl(mailbox, who)

   Delete the ACLs (remove any rights) set for who on mailbox.

IMAP4.enable(capability)

   Enable *capability* (see **RFC 5161**).  Most capabilities do not
   need to be enabled.  Currently only the "UTF8=ACCEPT" capability is
   supported (see **RFC 6855**).

   3.5 新版功能: The "enable()" method itself, and **RFC 6855**
   support.

IMAP4.expunge()

   Permanently remove deleted items from selected mailbox. Generates
   an "EXPUNGE" response for each deleted message. Returned data
   contains a list of "EXPUNGE" message numbers in order received.

IMAP4.fetch(message_set, message_parts)

   Fetch (parts of) messages.  *message_parts* should be a string of
   message part names enclosed within parentheses, eg: ""(UID
   BODY[TEXT])"".  Returned data are tuples of message part envelope
   and data.

IMAP4.getacl(mailbox)

   Get the "ACL"s for *mailbox*. The method is non-standard, but is
   supported by the "Cyrus" server.

IMAP4.getannotation(mailbox, entry, attribute)

   Retrieve the specified "ANNOTATION"s for *mailbox*. The method is
   non-standard, but is supported by the "Cyrus" server.

IMAP4.getquota(root)

   Get the "quota" *root*'s resource usage and limits. This method is
   part of the IMAP4 QUOTA extension defined in rfc2087.

IMAP4.getquotaroot(mailbox)

   Get the list of "quota" "roots" for the named *mailbox*. This
   method is part of the IMAP4 QUOTA extension defined in rfc2087.

IMAP4.list([directory[, pattern]])

   List mailbox names in *directory* matching *pattern*.  *directory*
   defaults to the top-level mail folder, and *pattern* defaults to
   match anything.  Returned data contains a list of "LIST" responses.

IMAP4.login(user, password)

   Identify the client using a plaintext password. The *password* will
   be quoted.

IMAP4.login_cram_md5(user, password)

   Force use of "CRAM-MD5" authentication when identifying the client
   to protect the password.  Will only work if the server "CAPABILITY"
   response includes the phrase "AUTH=CRAM-MD5".

IMAP4.logout()

   Shutdown connection to server. Returns server "BYE" response.

IMAP4.lsub(directory='""', pattern='*')

   List subscribed mailbox names in directory matching pattern.
   *directory* defaults to the top level directory and *pattern*
   defaults to match any mailbox. Returned data are tuples of message
   part envelope and data.

IMAP4.myrights(mailbox)

   Show my ACLs for a mailbox (i.e. the rights that I have on
   mailbox).

IMAP4.namespace()

   Returns IMAP namespaces as defined in **RFC 2342**.

IMAP4.noop()

   Send "NOOP" to server.

IMAP4.open(host, port)

   Opens socket to *port* at *host*.  This method is implicitly called
   by the "IMAP4" constructor.  The connection objects established by
   this method will be used in the "IMAP4.read()", "IMAP4.readline()",
   "IMAP4.send()", and "IMAP4.shutdown()" methods.  You may override
   this method.

IMAP4.partial(message_num, message_part, start, length)

   Fetch truncated part of a message. Returned data is a tuple of
   message part envelope and data.

IMAP4.proxyauth(user)

   Assume authentication as *user*. Allows an authorised administrator
   to proxy into any user's mailbox.

IMAP4.read(size)

   Reads *size* bytes from the remote server. You may override this
   method.

IMAP4.readline()

   Reads one line from the remote server. You may override this
   method.

IMAP4.recent()

   Prompt server for an update. Returned data is "None" if no new
   messages, else value of "RECENT" response.

IMAP4.rename(oldmailbox, newmailbox)

   Rename mailbox named *oldmailbox* to *newmailbox*.

IMAP4.response(code)

   Return data for response *code* if received, or "None". Returns the
   given code, instead of the usual type.

IMAP4.search(charset, criterion[, ...])

   Search mailbox for matching messages.  *charset* may be "None", in
   which case no "CHARSET" will be specified in the request to the
   server.  The IMAP protocol requires that at least one criterion be
   specified; an exception will be raised when the server returns an
   error.  *charset* must be "None" if the "UTF8=ACCEPT" capability
   was enabled using the "enable()" command.

   示例:

      # M is a connected IMAP4 instance...
      typ, msgnums = M.search(None, 'FROM', '"LDJ"')

      # or:
      typ, msgnums = M.search(None, '(FROM "LDJ")')

IMAP4.select(mailbox='INBOX', readonly=False)

   Select a mailbox. Returned data is the count of messages in
   *mailbox* ("EXISTS" response).  The default *mailbox* is "'INBOX'".
   If the *readonly* flag is set, modifications to the mailbox are not
   allowed.

IMAP4.send(data)

   Sends "data" to the remote server. You may override this method.

IMAP4.setacl(mailbox, who, what)

   Set an "ACL" for *mailbox*. The method is non-standard, but is
   supported by the "Cyrus" server.

IMAP4.setannotation(mailbox, entry, attribute[, ...])

   Set "ANNOTATION"s for *mailbox*. The method is non-standard, but is
   supported by the "Cyrus" server.

IMAP4.setquota(root, limits)

   Set the "quota" *root*'s resource *limits*. This method is part of
   the IMAP4 QUOTA extension defined in rfc2087.

IMAP4.shutdown()

   Close connection established in "open".  This method is implicitly
   called by "IMAP4.logout()".  You may override this method.

IMAP4.socket()

   Returns socket instance used to connect to server.

IMAP4.sort(sort_criteria, charset, search_criterion[, ...])

   The "sort" command is a variant of "search" with sorting semantics
   for the results.  Returned data contains a space separated list of
   matching message numbers.

   Sort has two arguments before the *search_criterion* argument(s); a
   parenthesized list of *sort_criteria*, and the searching *charset*.
   Note that unlike "search", the searching *charset* argument is
   mandatory.  There is also a "uid sort" command which corresponds to
   "sort" the way that "uid search" corresponds to "search".  The
   "sort" command first searches the mailbox for messages that match
   the given searching criteria using the charset argument for the
   interpretation of strings in the searching criteria.  It then
   returns the numbers of matching messages.

   This is an "IMAP4rev1" extension command.

IMAP4.starttls(ssl_context=None)

   Send a "STARTTLS" command.  The *ssl_context* argument is optional
   and should be a "ssl.SSLContext" object.  This will enable
   encryption on the IMAP connection.  Please read Security
   considerations for best practices.

   3.2 新版功能.

   在 3.4 版更改: The method now supports hostname check with
   "ssl.SSLContext.check_hostname" and *Server Name Indication* (see
   "ssl.HAS_SNI").

IMAP4.status(mailbox, names)

   Request named status conditions for *mailbox*.

IMAP4.store(message_set, command, flag_list)

   Alters flag dispositions for messages in mailbox.  *command* is
   specified by section 6.4.6 of **RFC 2060** as being one of "FLAGS",
   "+FLAGS", or "-FLAGS", optionally with a suffix of ".SILENT".

   For example, to set the delete flag on all messages:

      typ, data = M.search(None, 'ALL')
      for num in data[0].split():
         M.store(num, '+FLAGS', '\\Deleted')
      M.expunge()

   注解: Creating flags containing ']' (for example: "[test]")
     violates **RFC 3501** (the IMAP protocol).  However, imaplib has
     historically allowed creation of such tags, and popular IMAP
     servers, such as Gmail, accept and produce such flags.  There are
     non-Python programs which also create such tags.  Although it is
     an RFC violation and IMAP clients and servers are supposed to be
     strict, imaplib nonetheless continues to allow such tags to be
     created for backward compatibility reasons, and as of python 3.6,
     handles them if they are sent from the server, since this
     improves real-world compatibility.

IMAP4.subscribe(mailbox)

   Subscribe to new mailbox.

IMAP4.thread(threading_algorithm, charset, search_criterion[, ...])

   The "thread" command is a variant of "search" with threading
   semantics for the results.  Returned data contains a space
   separated list of thread members.

   Thread members consist of zero or more messages numbers, delimited
   by spaces, indicating successive parent and child.

   Thread has two arguments before the *search_criterion* argument(s);
   a *threading_algorithm*, and the searching *charset*.  Note that
   unlike "search", the searching *charset* argument is mandatory.
   There is also a "uid thread" command which corresponds to "thread"
   the way that "uid search" corresponds to "search".  The "thread"
   command first searches the mailbox for messages that match the
   given searching criteria using the charset argument for the
   interpretation of strings in the searching criteria. It then
   returns the matching messages threaded according to the specified
   threading algorithm.

   This is an "IMAP4rev1" extension command.

IMAP4.uid(command, arg[, ...])

   Execute command args with messages identified by UID, rather than
   message number.  Returns response appropriate to command.  At least
   one argument must be supplied; if none are provided, the server
   will return an error and an exception will be raised.

IMAP4.unsubscribe(mailbox)

   Unsubscribe from old mailbox.

IMAP4.xatom(name[, ...])

   Allow simple extension commands notified by server in "CAPABILITY"
   response.

The following attributes are defined on instances of "IMAP4":

IMAP4.PROTOCOL_VERSION

   The most recent supported protocol in the "CAPABILITY" response
   from the server.

IMAP4.debug

   Integer value to control debugging output.  The initialize value is
   taken from the module variable "Debug".  Values greater than three
   trace each command.

IMAP4.utf8_enabled

   Boolean value that is normally "False", but is set to "True" if an
   "enable()" command is successfully issued for the "UTF8=ACCEPT"
   capability.

   3.5 新版功能.


21.15.2. IMAP4 Example
======================

Here is a minimal example (without error checking) that opens a
mailbox and retrieves and prints all messages:

   import getpass, imaplib

   M = imaplib.IMAP4()
   M.login(getpass.getuser(), getpass.getpass())
   M.select()
   typ, data = M.search(None, 'ALL')
   for num in data[0].split():
       typ, data = M.fetch(num, '(RFC822)')
       print('Message %s\n%s\n' % (num, data[0][1]))
   M.close()
   M.logout()
