IMAP Protocol is used to configure gmail account in MAC Outlook. Using Gmail users can send, store and receive emails.
Gmail is a web based email service provider by Google. IMAP protocol never download emails on client machine ,emails are accessed from mail server directly. IMAP protocol contacts the mail server whenever user check the inbox email messages.
IMAP allows to access emails via different devices. IMAP stands for Internet Message Access Protocol is a popular internet protocol used by email clients and allow users to access email messages stored on mail server. Outlook for Mac Overview of IMAP Protocol and Gmail