Browse Prior Art Database

Distributed Electronic Mail Models in IMAP4 (RFC1733) Disclosure Number: IPCOM000003982D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 3 page(s) / 6K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Crispin: AUTHOR


Status of this Memo

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 51% of the total text.

Network Working Group M. Crispin

Request for Comments: 1733 University of Washington

Category: Informational December 1994


Status of this Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

Distributed Electronic Mail Models

There are three fundamental models of client/server email: offline,

online, and disconnected use. IMAP4 can be used in any one of these

three models.

The offline model is the most familiar form of client/server email

today, and is used by protocols such as POP-3 (RFC 1225) and UUCP.

In this model, a client application periodically connects to a

server. It downloads all the pending messages to the client machine

and deletes these from the server. Thereafter, all mail processing

is local to the client. This model is store-and-forward; it moves

mail on demand from an intermediate server (maildrop) to a single

destination machine.

The online model is most commonly used with remote filesystem

protocols such as NFS. In this model, a client application

manipulates mailbox data on a server machine. A connection to the

server is maintained throughout the session. No mailbox data are

kept on the client; the client retrieves data from the server as is

needed. IMAP4 introduces a form of the online model that requires

considerably less network bandwidth than a remote filesystem

protocol, and provides the opportunity for using the server for CPU

or I/O intensive functions such as parsing and searching.

The disconnected use model is a hybrid of the offline and online

models, and is used by protocols such as PCMAIL (RFC 1056). In this

model, a client user downloads some set of messages from the server,

manipulates them offline, then at some later time uploads the

changes. The server remains the authoritative repository of the

messages. The problems of synchronization (particularly when

multiple clients are involved) are handled through the means of

unique identifiers for each message.

Each of these models have their own strengths and weaknesses:

Feature Offline Online Disc

------- ------- ------ ----

Can use multiple clients NO YES YES

Minimum use of server connect time YES NO YES

Minimum use of server resources YES NO NO

Minimum use of client disk resources NO YES NO

Multiple remote mailboxes NO YES YES

Fast startup NO YES NO

Mail processing when not online YES NO YES

Although IMAP4 has its origins as a protocol designed to accommodate

the online model, it can suppo...