When a message reaches its destination server, it is written to the user??™s mailbox by the local MDA.
From that point, the message may be viewed by the user using one of three methods:
Direct access to the mailbox??”An MUA (mail user agent) with access to the mailbox
file, directly or through a network file system, can read messages from the disk and display
them for the user. This is generally a console or Web mail application running on the
server.
Downloaded to a workstation for local viewing??”Most mail users use POP3 (Post
Office Protocol, version 3) to download messages to their local computers and view them
in applications such as Evolution or Balsa. By default, messages are removed from the
server during this process (similar to when you get your ???snail mail??? from the mailbox).
Accessed interactively over the network??”Most clients also support viewing messages
while they are still on the server, through IMAP (Internet Message Access Protocol). Unlike
POP3, this protocol enables users to access multiple folders on their servers and also allows
them to access their messages from anywhere. However, this also creates a heavier burden
on the server because it must process (and store) everything that the user decides to keep.
Most Web mail applications use IMAP as their backend protocol for accessing mailboxes;
this eliminates the need for direct access to the mail files and makes it easier to split functions
between systems.
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