IMAP
also: IMAP4, Internet Message Access Protocol
IMAP (Internet Message Access Protocol) is a standard protocol for retrieving and managing email messages from a remote mail server, allowing clients to access messages while keeping them stored on the server.
IMAP enables email clients to connect to mail servers and download messages on-demand while maintaining synchronization across multiple devices. Unlike POP3, which typically downloads messages locally and removes them from the server, IMAP keeps emails on the server, making it ideal for users who check email from different devices.
With IMAP, you can organize messages into server-side folders, search messages without downloading them all, and maintain read/unread status across devices. For example, marking an email as read on your phone will show it as read on your desktop client because both connect to the same server.
IMAP uses port 143 by default (or port 993 for encrypted IMAPS connections). Common IMAP servers in Linux environments include Dovecot and Cyrus.