IMAP

networking

Stands for: Internet Message Access Protocol

A protocol for reading email kept on the server, across multiple devices.

Internet Message Access Protocol (RFC 9051) leaves messages on the server and syncs state (read, foldered) across clients, unlike POP3 which typically downloads and removes them.

IMAP keeps mail on the server and synchronizes state, so folders, read status and flags are consistent across every device. That is the property that makes it the right choice today, where POP3's download-and-delete model belongs to an era of one computer per person.

The cost is server-side storage and a chattier protocol, and the operational subtlety is that clients differ substantially in how aggressively they synchronize. A mailbox with hundreds of thousands of messages in one folder will perform badly on some clients and acceptably on others, which is why mailbox hygiene shows up as a support issue. IDLE is what provides push notification without polling, and a client that lacks it will poll instead and feel slower for reasons the user cannot see.

Also known as: imap

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