Here is our explanation of the differences between POP and IMAP.
We recommend and support use of IMAP.
POP (Post Office Protocol) was the original method to download and receive emails from the mail server to one computer, and that's it... one computer. As people started to buy multiple computers, there was a need to be able to access the same email messages on two computers or more. To address this issue, POP3 (revision 3) was invented. It has a feature to "leave the message on the server" but the problem with this is that the messages do not sync correctly between multiple computers, and there is no way to tell if a message has been read or not. You will only be able to check and download messages from the Inbox, and there are no syncing capabilities for other folders or accessing the server's Junk Email folder. Lastly with POP3, you have to manually check for new messages, which is not good if you need to receive emails right away.
IMAP (Internet Message Access Protocol) was invented to address the shortcomings of POP3. Now in its 4th revision, IMAP4 is capable of leaving messages on the server, can delete or undelete messages, can synchronize messages between every device you have, sync folders, retrieve messages from the Junk Email folder, and tell you if a message has been read or not. This enables you to synchronize your emails and folders between a desktop, a laptop, Webmail, and a mobile phone or tablet - all at the same time. To take things one step further, the IDLE command was invented to "PUSH" email messages to your inbox in real-time. This is called IMAP-IDLE and any device that supports it will get emails instantly in its inbox.
The main difference between the two is POP3 downloads messages to your computer where IMAP4 keeps it on our server. If you use POP3 and your computer crashes, you could lose all your emails if you did not properly back them up. Our servers on the other hand were built from the ground up to be "mission critical." The odds of our servers going down is less likely than being hit by lightning. Plus, in order to take advantage of our Webmail Interface, use PUSH Email, and be able to synchronize email and folders on as many devices as you have, you must use IMAP. Remember, our server filters spam and puts them in the Junk Email folder. If you are using POP3, you can only access the Inbox so you will never be able to see messages in the Junk Email folder, which can lead to missing email messages.
So, unless you absolutely know what you are doing and must use POP3 for some reason, we strongly recommend using the IMAP protocol for your email communications on any device or software.