POP3 clients hide virtually all server-side details from the user. While this makes the clients easy to use, it hides reality to such an extent that users can unwittingly stress the server's resources. Even user problems tend to be masked by a client until "all of a sudden" you experience sporadic and eventually regular mail connection failures.
This document can help ensure that you are able to receive your mail quickly and reliably. Two alternative strategies are to optimize one's POP client for performance or to reconfigure the client for IMAP instead of POP.
Optimizing a POP Client
Keep Old, Invisible Messages from Accumulating on the Server
As we've seen, it does not suffice to delete individual messages from the desktop. Instead, the mail client must be given a global configuration that removes old server-side messages.
The basic configuration item is an entry that can be toggled on and off, to the effect that old messages are to be kept on the server. Do not let this be your configuration!
Some POP3 clients, e.g. Eudora Pro, offer variations of this basic item. These may include offering to delete old server-side messages after a specified number of days, or to delete server-side messages whenever they are deleted from the desktop trash. There are no known instances of success with the latter setting, so it should be avoided. Specifying a number of days, on the other hand, works well. (This setting is safe even when one doesn't read mail for a longer time interval, because only previously read messages are removed.) For users who want their server side mail on tape backups, even over 3-day weekends, a minimum setting of 4 days is recommended.
Check Less Often for New Mail
POP3 transactions of more than 5 minutes duration are not unusual. To avoid having your client attempt a new transaction before the previous one is finished, with unpredictable results, it is recommended you check for new mail no more frequently than every 10 or, even better, 15 minutes. Although it is less important than cleaning out your server side mailbox, this can prevent download failures in "borderline" cases.
Specific Configuration Settings
In Eudora Pro 4.x for Windows, pull down Tools / Options, click the Incoming Mail category and uncheck the Leave mail on server option. Click the Checking Mail category to set the frequency to at least 10 minutes.
In Netscape Messenger 4.0x for Windows, pull down Edit / Preferences, expand the Mail & News heading, select Mail Servers, and uncheck the Leave messages on server option. Set the Check for mail frequency to at least 10 minutes.
In Netscape Messenger 4.5 for Windows, pull down Edit / Preferences, expand the Mail & News heading, select Mail Servers, click the Edit button, select the POP tab, and uncheck the Leave messages on server option.
Switching from POP to IMAP
Many mail clients now offer IMAP4 as an alternative to POP3. Under IMAP, the messages you see and manipulate are the server-side copies; messages are only brought onto the desktop host when saved to a desktop folder.
In addition to a server-side view, IMAP offers more efficient downloads: Instead of using POP3's "one big gulp," IMAP can transfer messages individually. Our IMAP configuration page contains a more detailed comparison of IMAP and POP, as well as IMAP configuration instructions.
A potential drawback of IMAP is lack of support for the encrypted APOP authentication of POP clients such as Eudora Pro. However, other available authentication techniques are more secure than APOP. See our IMAP configuration page for links to detailed configuration instructions that include such authentication.
If you save a message to a non-default folder using IMAP, POP will not be able to find that folder. Otherwise, one can switch between the two protocols at will.