Information Technology Reference
In-Depth Information
• First, your client (that is, your email program) asks the server for the list of mes-
sages in your Inbox.
• Then, depending on your client's capabilities and settings, it downloads either
all the messages, just the messages you select, or all messages under a specified
size, to your local device.
• Finally (and optionally), your client instructs the server to delete the server copy
of some or all of the messages.
The server doesn't keep track of whether a message has been downloaded, read, or deleted;
only your client knows this, and the assumption underlying the protocol is that you want to
read, organize, and store your mail on a single device, using the server only as a conduit to re-
ceive your mail. If you want to store any messages in mailboxes other than your Inbox, when
you create those mailboxes in your email client, they're stored locally (not on the server); the
messages you move to these mailboxes are thus also stored locally.
You can usually set your client to leave messages on the server (rather than delete them im-
mediately after retrieving them) and then check your email with a different client (or on a
different device), but all those messages will appear to be “new” and unread on every other
client or device. This, among other reasons, makes POP a poor option if you work with email
on multiple computers and devices.
In addition, although iOS supports POP, iOS Mail doesn't let you create new mailboxes to file
messages locally. That means an iOS device doesn't work well as the
sole
device used with a
POP account, and because POP works best when used with a single device, this mismatch of
capabilities makes POP less than ideal for an iOS device.
IMAP
From a user's point of view, the main distinction between POP and IMAP is that by default in
an IMAP account, messages stay on the mail server even after you've downloaded and read
them. You can create mailboxes on the server for filing messages, and those mailboxes are
mirrored in all your client(s), on all your devices. (Nothing prevents you from moving mes-
sages off the server and into mailboxes that are stored only locally, if that's your preferen-
ce—but by doing so you lose most of the IMAP advantages for those messages since they'll no
longer sync to your other clients and devices.)
In addition, the server—not your local client—keeps track of which messages you've read, for-
warded, or replied to, so you see the correct status indicators even if you check your email
from another client or device. You can, of course, delete messages you no longer want in or-
der to free up space on the server; doing so deletes the message from all devices. Although
each client and provider handles deletions somewhat differently, deleting a message typically