IMAP (Internet Message Access Protocol) is a protocol for retrieving email messages from a mail server. It allows a client (such as an email program on a computer or smartphone) to access email messages that are stored on the server, without the need to download the messages to the client device.
IMAP provides several features that make it useful for accessing email messages. For example, it allows the client to search for specific messages on the server, and to download only the messages that match certain criteria (such as messages from a particular sender or messages with a certain subject). IMAP also allows the client to retrieve only the headers of email messages, rather than the entire message, which can save time and bandwidth.
IMAP is typically used with an email program that supports the IMAP protocol, such as Microsoft Outlook or Apple Mail. It can also be used with web-based email services, such as Gmail or Yahoo! Mail, by accessing the email service through a web browser.