When emails are coming to you from different sources, the two commonly used protocols are POP or Post Office Protocol and IMAP or Internet Message Access Protocol. One of the major differences between the two is that IMAP is the newer of the two. Though both are more reliable, since IMAP is more recent, and it is often used by people when retrieving their emails.
Although both serve the same function, however, both differ greatly when it comes to how they implement their functions. For instance, when you use IMAP, it reads and downloads all the messages in the server without deleting anything on the server. In contrast, when you use POP, it gets you all the messages in the server without leaving anything on the server.
Another difference is that, once you are connected to the mail server using IMAP, it keeps you connected unless you decide to log out, whereas POP will get you disconnected as soon as the emails are read.