POP3
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. This choice is handy when you have an email storage quota on your mail server, or you prefer to retain all of your messages locally on your PC/device so that they can be accessed offline.
Once downloaded, you can read messages retrieved with POP anytime without reconnecting to the Internet. You can only access previously read messages from the PC/device you downloaded them on. In a multiple PC/device environment, this can be a problem.
IMAP
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 PC/device. This is advantageous if you access your mail from multiple PC’s/devices, or if you expect to need access to your mail from any computer on the world-wide-web (webmail).
Checking your mail with a client or web-based environment using this protocol will allow you retain your emails in a universally accessible place for access whenever and wherever you need them. IMAP supports the use of folders for mail organization, but instead of organizing the emails on your local computer, the folders are kept on the server as well. Another advantage to IMAP is quicker access to mail.
One drawback to using IMAP and saving emails on the server is that you will be restricted by your accounts email quota (64MB for PILOT, 512MB for STARTER CLOUD and 1024MB for BUSINESS and BUSINESS CLOUD plans) . Once you have stored enough emails to fill your quota, emails will be returned to the sender
Please Note: You may have a maximum of 20 IMAP connections to the server at one time.