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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
TCP/IP Electronic Mail Mailbox Access Model, Method and Protocol Overview
(Page 2 of 3)
E-Mail Access and Retrieval Models
For the reasons just examined, there
is an advantage to providing more than one way to access a mailbox.
RFC 1733, Distributed Electronic Mail Models In IMAP4,
describes three different paradigms or models for mail access and retrieval:
- Online Access Model: This is the mode
of access that we would all be using in my ideal world scenario,
where every machine was always connected to the Internet running an
SMTP server. You would have constant, direct online access to your mailbox.
In the real world, this model is still used by some Internet users,
especially those who have UNIX accounts or run their own SMTP servers.
I call this direct server access.
- Offline Access Model: In this paradigm,
a user establishes a connection to a server where his or her mailbox
is located. The user downloads received messages to the client device,
and then deletes them from the server mailbox. All reading and other
activity performed on the mail can be done offline once
the mail has been retrieved.
- Disconnected Access Model: This is a hybrid
of online and offline access. The user downloads messages from the server,
so he or she can read or otherwise manipulate them without requiring
a continuous connection to the server. However, the mail is not
deleted from the server, like in the offline model. At some time in
the future, the user connects back with the server and synchronizes
any changes made on the local device with the mailbox on the server.
What sort of changes? Examples include marking whether or not a message
has been read, to keep track of unread mail, and marking messages to
which the user has already replied. These are important tools to help
those with busy mailboxes keep track of what they need to do.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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