NAME

pop3 - Tcl client for POP3 email protocol

Table Of Contents

• Table Of Contents

• Synopsis

• Description

• TLS Security Considerations

• API

• Secure mail transfer

• Bugs, Ideas, Feedback

• Keywords

• Category

SYNOPSIS

package require Tcl 8.4
package require pop3 ?1.9?

::pop3::open ?-msex 0|1? ?-retr-mode retr|list|slow? ?-socketcmd cmdprefix? ?-stls 0|1? ?-tls-callback stls-callback-command? host username password ?port?
::pop3::config chan
::pop3::status chan
::pop3::last chan
::pop3::retrieve chan startIndex ?endIndex?
::pop3::delete chan startIndex ?endIndex?
::pop3::list chan ?msg?
::pop3::top chan msg n
::pop3::uidl chan ?msg?
::pop3::capa chan
::pop3::close chan

DESCRIPTION

The pop3 package provides a simple Tcl-only client library for the POP3 email protocol as specified in RFC 1939. It works by opening the standard POP3 socket on the server, transmitting the username and password, then providing a Tcl API to access the POP3 protocol commands. All server errors are returned as Tcl errors (thrown) which must be caught with the Tcl catch command.

TLS Security Considerations

This package uses the TLS package to handle the security for https urls and other socket connections.

Policy decisions like the set of protocols to support and what ciphers to use are not the responsibility of TLS, nor of this package itself however. Such decisions are the responsibility of whichever application is using the package, and are likely influenced by the set of servers the application will talk to as well.

For example, in light of the recent POODLE attack discovered by Google many servers will disable support for the SSLv3 protocol. To handle this change the applications using TLS must be patched, and not this package, nor TLS itself. Such a patch may be as simple as generally activating tls1 support, as shown in the example below.

package require tls
tls::init -tls1 1 ;# forcibly activate support for the TLS1 protocol

... your own application code ...

API

• ::pop3::open ?-msex 0|1? ?-retr-mode retr|list|slow? ?-socketcmd cmdprefix? ?-stls 0|1? ?-tls-callback stls-callback-command? host username password ?port?

  Open a socket connection to the server specified by host, transmit the username and password as login information to the server. The default port number is 110, which can be overridden using the optional port argument. The return value is a channel used by all of the other ::pop3 functions.

  The command recognizes three options

  • -msex boolean

    Setting this option tells the package that the server we are talking to is an MS Exchange server (which has some oddities we have to work around). The default is False.

  • -retr-mode retr|list|slow

    The retrieval mode determines how exactly messages are read from the server. The allowed values are retr, list and slow. The default is retr. See ::pop3::retrieve for more information.

  • -socketcmd cmdprefix

    This option allows the user to overide the use of the builtin socket command with any API-compatible command. The envisioned main use is the securing of the new connection via SSL, through the specification of the command tls::socket. This command is specially recognized as well, changing the default port of the connection to 995.

  • -stls boolean

    Setting this option tells the package to secure the connection using SSL or TLS. It performs STARTTLS as described in IETF RFC 2595, it first opens a normal, unencrypted connection and then negotiates a SSLv3 or TLSv1 connection. If the connection cannot be secured, the connection will be closed and an error will be returned

  • -tls-callback stls-callback-command

    This option allows the user to overide the tls::callback used during the -stls SSL/TLS handshake. See the TLS manual for details on how to implement this callback.

• ::pop3::config chan

  Returns the configuration of the pop3 connection identified by the channel handle chan as a serialized array.

• ::pop3::status chan

  Query the server for the status of the mail spool. The status is returned as a list containing two elements, the first is the number of email messages on the server and the second is the size (in octets, 8 bit blocks) of the entire mail spool.

• ::pop3::last chan

  Query the server for the last email message read from the spool. This value includes all messages read from all clients connecting to the login account. This command may not be supported by the email server, in which case the server may return 0 or an error.

• ::pop3::retrieve chan startIndex ?endIndex?

  Retrieve a range of messages from the server. If the endIndex is not specified, only one message will be retrieved. The return value is a list containing each message as a separate element. See the startIndex and endIndex descriptions below.

  The retrieval mode determines how exactly messages are read from the server. The mode retr assumes that the RETR command delivers the size of the message as part of the command status and uses this to read the message efficiently. In mode list RETR does not deliver the size, but the LIST command does and we use this to retrieve the message size before the actual retrieval, which can then be done efficiently. In the last mode, slow, the system is unable to obtain the size of the message to retrieve in any manner and falls back to reading the message from the server line by line.

  It should also be noted that the system checks upon the configured mode and falls back to the slower modes if the above assumptions are not true.

• ::pop3::delete chan startIndex ?endIndex?

  Delete a range of messages from the server. If the endIndex is not specified, only one message will be deleted. Note, the indices are not reordered on the server, so if you delete message 1, then the first message in the queue is message 2 (message index 1 is no longer valid). See the startIndex and endIndex descriptions below.

  • startIndex

    The startIndex may be an index of a specific message starting with the index 1, or it have any of the following values:

    • start

      This is a logical value for the first message in the spool, equivalent to the value 1.

    • next

      The message immediately following the last message read, see ::pop3::last.

    • end

      The most recent message in the spool (the end of the spool). This is useful to retrieve only the most recent message.

  • endIndex

    The endIndex is an optional parameter and defaults to the value "-1", which indicates to only retrieve the one message specified by startIndex. If specified, it may be an index of a specific message starting with the index "1", or it may have any of the following values:

    • last

      The message is the last message read by a POP3 client, see ::pop3::last.

    • end

      The most recent message in the spool (the end of the spool).

• ::pop3::list chan ?msg?

  Returns the scan listing of the mailbox. If parameter msg is given, then the listing only for that message is returned.

• ::pop3::top chan msg n

  Optional POP3 command, not all servers may support this. ::pop3::top retrieves headers of a message, specified by parameter msg, and number of n lines from the message body.

• ::pop3::uidl chan ?msg?

  Optional POP3 command, not all servers may support this. ::pop3::uidl returns the uid listing of the mailbox. If the parameter msg is specified, then the listing only for that message is returned.

• ::pop3::capa chan

  Optional POP3 command, not all servers may support this. ::pop3::capa returns a list of the capabilities of the server. TOP, SASL, UIDL, LOGIN-DELAY and STLS are typical capabilities. See IETF RFC 2449.

• ::pop3::close chan

  Gracefully close the connect after sending a POP3 QUIT command down the socket.

Secure mail transfer

A pop3 connection can be secured with SSL/TLS by requiring the package TLS and then using either the option -socketcmd or the option -stls of the command pop3::open. The first method, option -socketcmd, will force the use of the tls::socket command when opening the connection. This is suitable for POP3 servers which expect SSL connections only. These will generally be listening on port 995.

package require tls
tls::init -cafile /path/to/ca/cert -keyfile ...

# Create secured pop3 channel
pop3::open -socketcmd tls::socket \
	$thehost $theuser $thepassword

...

The second method, option -stls, will connect to the standard POP3 port and then perform an STARTTLS handshake. This will only work for POP3 servers which have this capability. The package will confirm that the server supports STARTTLS and the handshake was performed correctly before proceeding with authentication.

package require tls
tls::init -cafile /path/to/ca/cert -keyfile ...

# Create secured pop3 channel
pop3::open -stls 1 \
	$thehost $theuser $thepassword

...

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category pop3 of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

KEYWORDS

email, mail, pop, pop3, rfc 1939, secure, ssl, tls

CATEGORY

Networking