IMAP ( Internet Message Access Protocol) is a standard email protocol that stores email messages on a mail server.
It allows the end user to view and manipulate the messages as though they were stored locally on the end user’s computing device(s)
IMAP was designed with the goal of permitting complete management of an email box by multiple email clients, therefore clients generally leave messages on the server until the user explicitly deletes them. An IMAP server typically listens on port number 143. IMAP over SSL (IMAPS) is assigned the port number 993.