What is IMAP?

IMAP (Internet Message Access Protocol) is an Internet protocol for storing and retrieving e-mail messages.

Using IMAP, e-mails can be retrieved from various Internet-enabled end devices at any time, as long as they are online. Unlike POP3 (a similar protocol), synchronization on the end device occurs in parallel with the mail server. Thus, absolutely identical information about your e-mail messages can be found on all devices (smartphone, tablet, desktop, webmail, etc.).

Edits are taken over directly, both on the mail server and in the email client. Also, it is not necessary to download all the emails, as here you can open individual messages directly from the mailbox.

However, with IMAP it can happen that the mailbox overflows if no e-mails are deleted. In addition, access to the mailbox is also not possible without an Internet connection.

For modern email systems, the use of IMAP is recommended over POP3 because most people use multiple email clients to retrieve mail and only with IMAP there is data consistancy everywhere.

See also:
Wikipedia: IMAP