What is the difference between pop3, IMAP and Exchange?

POP3 - Emails are downloaded from email server and saved locally. Inbox and sent items emails are not available on the mail server

IMAP - Emails are downloaded from email server and saved locally (We can save a copy of inbox emails on the mail server when we check save a copy on the exchange server while configuring IMAP). Sent items emails are available only on local server whereas inbox items could be accessed anywhere

EXCHANGE - All the Email (Incoming and Sent Items) is stored on the central Exchange mail server which can be accessed via outlook, web mail or active sync. Emails can be accessed anywhere anytime. Syncs calendar, contacts as well