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The TCP/IP Guide
9 TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
9 TCP/IP Key Applications and Application Protocols
9 TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
9 TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
9 TCP/IP Electronic Mail Access and Retrieval Protocols and Methods
9 TCP/IP Internet Message Access Protocol (IMAP/IMAP4)
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IMAP Overview, History, Versions and Standards
(Page 2 of 3)
IMAP Features
In the mid-1980s, development began
at Stanford University on a new protocol that would provide a more capable
way of accessing user mailboxes. The result was the Interactive Mail
Access Protocol, later renamed the Internet Message Access Protocol
(IMAP). IMAP was designed for the specific purpose of providing
flexibility in how users access e-mail messages. It in fact can operate
in all three of the access modes: online, offline and disconnected access.
Of these, it is the online and disconnected access modes that are of
interest to most users of the protocol; offline access is similar to
how POP works.
IMAP allows a user to do all of the
following:
- Access and retrieve mail from a remote server
so it can be used locally while retaining it on the server.
- Set message flags so that the user can keep track
of which messages he or she has already seen, already answered, and
so on.
- Manage multiple mailboxes and transfer messages
from one mailbox to another. You can organize mail into categories,
which is useful for those working on multiple projects, those who are
on various mailing lists and so forth.
- Determine information about a message prior to
downloading it, to decide whether or not to retrieve it.
- Download only portions of a message, such as
one body part from a MIME
multipart message. This can be quite helpful
in cases where large multimedia files are combined with short text elements
in a single message.
- Manage documents other than e-mail. For example,
IMAP can be used to access Usenet
messages.
Of course, there are some disadvantages
to IMAP, but not many. One is that it is more complex, but it's really
not that complex, and the protocol has been around for
enough years that this is not a big issue. The most important sticking
point with IMAP is simply that it is used less commonly than POP, so
providers that support it are not as easy to find as those that support
POP. This is changing, however, as more people discover IMAP's benefits.
 Key Concept: The Post Office Protocol is popular because of its simplicity and long history, but POP has few features and normally only supports the rather limited offline mail access method. To provide more flexibility for users in how they access, retrieve and work with e-mail messages, the Internet Message Access Protocol (IMAP) was developed. IMAP is primarily used in the online and disconnected access models; it allows users to access mail from many different devices, manage multiple mailboxes, select only certain messages for downloading, and much more. Due to its many capabilities, it is growing in popularity.
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Version 3.0 - Version Date: September 20, 2005
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