POP (or POP3) stands for Post Office Protocol. This mail delivery protocol was the standard for a number of years, particularly when server-side storage space came at a premium.
Most distinctively, a client using POP to check email will retrieve all of the messages from the server and store them on the local computer before opening or reading any of them. (You may select an option not to delete these messages from the server with most clients; doing so will cause you to download these messages again each time your check your mail). This choice is handy when you have an inconveniently small storage quota on your mail server, or you prefer to retain all of your messages locally so that they can be accessed offline.
Once downloaded, you can read messages retrieved with POP anytime without reconnecting to the Internet. The biggest drawback to this, for many, is that you can only access previously read messages from the computer you downloaded them on. In a multiple-computer environment, this can be a severe disadvantage.
For more information on the POP protocol, visit: http://en.wikipedia.org/wiki/POP3
IMAP stands for Internet Mail Access Protocol. The most distinctive feature of IMAP is that your mail messages remain on the server, instead of being downloaded to your computer. This is advantageous if you access your mail from multiple computers (such as an Open Access Lab environment), or if you expect to need access to your mail from any computer on the world wide web.
Checking your mail with a client or web-based environment using this protocol will allow you retain your messages in a universally accessible place for access whenever and wherever your need them. IMAP supports the use of folders for mail organization, but instead of organizing the messages on your local computer, the folders are kept on the server as well. Another advantage to IMAP is quicker access to mail. If you access your email from a slower connection, such as modem dial-up, you will notice a substantial increase in speed; only the message headers are initially downloaded, so you can choose to download, open, and read only those messages of interest to you at that time.
One drawback to using IMAP and saving messages on the server is that you will be restricted by any quota limitation the administrator may set. Once you have stored enough messages to fill your quota, email may be returned to the sender.
For more information on the IMAP protocol, visit: http://en.wikipedia.org/wiki/Internet_Message_Access_Protocol
Please Note: You may have a maximum of 5 IMAP connections to the server at one time. Having more than 5 connections places a heavy load on the server and can result in your account being suspended.
If you would like more information on how to set up email connections using various different email programs, HostPapa has a wide variety of video tutorials: http://hostpapasupport.com/tutorials/Tutorials_eMail.shtml