Internet Message Access Protocol IMAP

Or, on a Solaris platform: telnet sunhost 110 Trying… Connected to sunhost. Escape character is ]. +OK sunhost Solstice tm Internet Mail Server tm POP3 2.0 at Sun, 3 Jan 1999 19:19:41 −0500 EST quit +OK BYE Connection closed by foreign host. Limitations — popper copies the users entire maildrop to the temporary directory tmp and then operates on that copy. If the maildrop is particularly large, or if inadequate space is available in tmp, then the daemon will refuse to continue and will terminate the connection. This is important to keep in mind if huge e−mail messages are expected.

20.5.2.2 Internet Message Access Protocol IMAP

Internet Message Access Protocol IMAP is another language that mail clients predominantly PC and Macintosh workstations use, this time in an interactive communication with an appropriate mail server usually an UNIX system. It is a method of accessing e−mail or bulletin board messages that are kept on a mail server. IMAP was designed to include POP capabilities and adds support for online and disconnect modes of remote mailbox access. IMAP version 4 is defined in RFC 1730. IMAP can also do offline mail processing, but its main functionality is in the online and disconnect modes of operation. Essentially, IMAP was designed to permit manipulation of remote mailboxes as if they were local to the user. Depending on the mail clients implementation of IMAP and the mail server administration, the user may either save messages onto the client machine, or save them on the mail server. IMAP is a more complex protocol to implement than POP; however, IMAP has several advantages over POP. Key goals for IMAP include: Be fully compatible with Internet messaging standards, e.g., MIME. • Allow message access and management from more than one computer. • Allow access without reliance on less efficient file access protocols. • Provide support for online, offline, and disconnected access modes. • Support concurrent access to shared mailboxes. • Client software needs no knowledge about the servers file store format. • IMAP includes operations for creating, deleting, and renaming mailboxes; checking for new messages; permanently removing messages; setting and clearing flags; MIME parsing so clients do not need to and searching; and selective fetching of message attributes, texts, and portions thereof for efficiency. More specifically, IMAP allows: Manipulation of persistent message status flags, such as Seen, Deleted, Answered, as well as user−defined flags • Storage of messages as well as fetching them; a message from an incoming message folder can be appended to an archive folder, or vice versa • 497 Processing of non−e−mail data, like NetNews or documents; this is very handy for uniformly accessing different classes of information • Offline access mode for minimum connect time and server resources; useful in situations where the only access to the mail server is via expensive dialup connections, and multiplatform access to the mailboxes is not needed • Permits online performance optimization, especially over low−speed links • IMAP was originally developed in 1986 at Stanford University. However, it garnered wide attention almost a decade later, and today IMAP is implemented in more and more software products. It is still not as well−known as earlier−released and less−capable alternatives such as POP. There is a companion protocol to IMAP, called Internet message support protocol IMSP, defined for user configuration management. IMSP permits the same location−independent multiplatform access to personal configuration data such as address books, bookmark lists, etc. that IMAP offers for mailboxes.

20.5.2.3 Comparing POP vs. IMAP