The most popular protocol for accessing a mailbox is the Post Office Protocol (POP) defined in rfc1939.While it is popular pop has very few features. It doesn't allow you to manage the mail on the server itself, instead you usually just download all mail to your local machine. A much more powerful protocol called the Internet Message Access Protocol (IMAP) was defined in the 1996 document rfc2060. With imap you can work with your mail while it's on the server and can create folders on the server in which to archive your mail. Thus the server itself can be the message store which is useful if you want to access your mail from more than one machine. You are not required to use the server to archive your mail with imap, you can use it like pop and download all the mail to your local machine.

Sending email is done via the Simple Mail Transfer Protocol (SMTP). You can use smtp to send mail directly to the destination but typically this is not done because the destination machine may be down or unreachable at the time you wish to send the mail. Most organizations have a local mail server that is up and reachable all of the time. You can use smtp to send your letter to that local mail server and it will then take over the job of getting the mail to the destination (which will may involve queueing the message and retrying to send it over a period of days).

• imap.cl - imap and pop client code.
• smtp.cl - smtp client code
• The Lesser Gnu Public License with the concept of a library defined by this preamble.
• ChangeLog - describe the modfications to the code

The postoffice source code is licensed under the terms of the Lisp Lesser GNU Public License, known as the LLGPL. The LLGPL consists of a preamble and the LGPL. Where these conflict, the preamble takes precedence. postoffice is referenced in the preamble as the LIBRARY.