Panix Help System: Why we recommend IMAP

The preferred modern method of connecting to mailservers is IMAP ("Internet Message Access Protocol"), as opposed to POP ("Post Office Protocol"), which you may have been using up until now. IMAP is far better suited to the modern assumption of persistent network connections (whether wired or not), of abundant server-side diskspace, and to the increasing ubiquity of handheld and portable network access devices (e.g. netbooks, smartphones, etc.).

IMAP works by essentially turning the mail client into a terminal or browser continuously connected to the mailserver. The mail itself does not get downloaded (unless the client is specifically instructed to transfer messages from the remote server into a local folder); only the headers do. The benefits are:

A faster connection; one need not wait for the mail to be downloaded.
The Inbox is updated automatically in real time, rather than only after a connection is initiated and completed.
Mail is no longer relegated by default to a specific client machine. It is accessible anywhere a network connection is available, for as long as it is left on the server.
Storage on the client machine need not be taxed. This is especially crucial with most smartphones, on which space is at a premium.
Multiple IMAP clients can access a single mailbox simultaneously without corrupting the mailbox..

Some historical context for POP:

Up until relatively recently, the prevailing of retrieving mail using what used to be called an "offline mail client" (such as Outlook, Thunderbird, and their ilk) was the "Post Office Protocol," or "POP". POP would form a temporary connection with a mailserver, download all the mail in one batch, delete it from the server, and disconnect. Mail could then be read while the local machine was offline (hence the earlier terminology).

This was the favored method when the common conditions included a) limited availability of diskspace on shared mailservers and b) non-persistent dialup connections (usually tying up a voice line).

There were (and are) several disadvantages to POP:

With sufficiently large quantities of mail, retrieval can take a long time, or fail entirely.
The burden of storage is moved to the local machine.
Unless the mail client were specifically instructed to leave mail on the server, downloaded messages are only accessible on a single client machine. This can be a problem if you need to access your mail "in the field," but your home computer is automatically downloading mail at regular intervals.
If, for whatever reason, the connection to the server is severed, the download must begin anew. This can result in duplicate messages being downloaded.

For these reasons, we strongly advise switching to IMAP.