Managing IMAP

IMAP’s Three Interaction Models

IMAP has three models for interacting with your mail: offline, online, and disconnected. The three interaction models are at the core of why, on its own merit, IMAP is the most powerful and flexible mail access protocol. The models are formally defined in RFC 1733 (Distributed Electronic Mail Models in IMAP4 ). Let’s take look at the three models.

The Online Model

In the online model, messages are left on the mail server and are manipulated remotely by mail client programs. The mail client maintains an open connection to the server for the duration of the session, that is, until the user decides to end the session.

Whether you prefer the online model has much to do with where you think the higher resource burden should be placed: on the client or on the server. If you believe, as we do, that resources are best centralized when possible, then you’re likely to prefer the online model. If you believe that centralized resources should be conserved whenever possible, even at the expense of a greater investment on the part of the user, then you’re likely to prefer the offline model. Watch out, though, because placing resource demands on the server requires attention and monitoring of system administrators lest things get out of hand. The online model can put a burden on memory and CPU resources if users tend to keep several mailboxes open, or if mail clients are poorly behaved in some way that results in multiple sessions per user.

In situations ...