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15.5.2 IMAP4 states
The disconnected model is a combination of both the offline and online models.
In this model, an IMAP4 client connects to a server, downloads some or all of the
messages, and disconnects. However, following the disconnect, the server does
not delete the messages as it does in the offline model. The client can then
manipulate the messages on the local system and later reconnect to the server.
Upon reconnecting, the client’s changes are synchronized with the server’s
mailbox, enacting any of the changes made while offline. In this model, the
server remains the authoritative repository for the messages.
Each of these models have advantages and disadvantages, but because IMAP4
supports all these models, the client is able to switch to another model to meet
whatever needs might exist at the time. Some of these advantages and
disadvantages are listed in Table 15-5.
Table 15-5 Advantages and disadvantages of the IMAP4 models
Feature Offline Online Disc
Use of multiple clients simultaneously No Yes Yes
Minimum use of server connection time Yes No Yes
Minimum use of server resources Yes No No
Minimum use of client resources No Yes No
Multiple remote mailboxes No Yes Yes
Fast startup No Yes No
Mail processing when not online Yes No Yes
Similar to POP3 (see 15.4.1, “Connection states” on page 589), the IMAP4
session exists in different states. Some commands are valid for certain states
and some of the commands are valid for all states. If the client sends a command
that is not appropriate for that state, the server responds with an error message.
The four states are:
Non-authenticated state In this state, the client has not yet authenticated
with the server.
Authenticated state In this state, the client has identified itself to the
server, and must select a mailbox to proceed.
Selected state In this state, a mailbox has been successfully
selected, and actions can be taken against mail
within the mailbox.
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