Internet Message Access Protocol (IMAP) is a standard email protocol, first widely deployed in the 1980s, that stores email messages on a mail server, but allows the end user to view and manipulate the messages as though they were stored locally on the end user’s computing device. This can help employees at a business to organize messages into specific folders, let clients know which email have been read, flagged for urgency, or follow-up and save draft messages on the server.
Source: TechTarget
Additional Reading: Where does IMAP Security Fall Short?
What should an SMB Owner do with IMAP?
Many businesses have left IMAP for webmail services such as GSuite and O365 because they generally are far more secure than IMAP. They provide encrypted access, two-factor authentication, and robust services that have far exceeded the capabilities of IMAP. If your business is still relying on IMAP, get off of it today!