Choosing IMAP or POP
You should use IMAP if:
You check your email with different computers or devices
IMAP lets you keep all of your messages, file attachments and folders in sync, and remembers the condition that you last left them in (read, replied, forwarded, and so on).
You use Web Mail in addition to an email program such as Outlook
IMAP lets you keep all of your messages, file attachments and folders synchronized between Web Mail and your email program.
You use SpamShield Pro
IMAP works with SpamShield Pro so you can filter out junk email before you download the entire message.
You want the peace of mind of having your email backed up
IMAP messages, file attachments and folders archived online are automatically backed up.
You use a slow connection to the Internet
IMAP lets you selectively download messages and file attachments.
You use a computer or device with limited storage space
IMAP lets you store messages and file attachments online and lets you selectively download only the ones that you need.
You currently use POP configured to leave messages on the server
IMAP leaves the messages on the server already. Thus you avoid the pitfalls POP accidentally removing messages from the server.
Instead, you may want to use POP if:
You check your email exclusively with one computer
You perform your own email backups
You must use an email program that does not work with IMAP
You used POP before and are satisfied with its limitations