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IMAP IDLE is an extension to the IMAP protocol that enables real-time email notifications without constant polling. When enabled, the email client maintains a persistent connection to the server and receives instant push notifications when new messages arrive. This eliminates the need to manually refresh or poll at fixed intervals, reducing server load and battery consumption while ensuring immediate email delivery awareness.
IMAP IDLE transforms email from a pull-based to a push-based system. Without IDLE, email clients must poll the server at regular intervals (every 5-15 minutes), creating unnecessary network traffic and server load. With IDLE, you receive emails instantly like a messaging app, improving response times and user experience. For mobile devices, IDLE significantly reduces battery drain compared to frequent polling, making it essential for modern email applications.
When an email client supports IMAP IDLE, it sends an IDLE command to the mail server after selecting a mailbox. The server keeps the connection open and notifies the client immediately when changes occur (new messages, deletions, or flag changes). The client must send a DONE command to exit IDLE mode before performing other operations. Most implementations renew the IDLE connection every 29 minutes to prevent timeout, as RFC 2177 recommends servers allow at least 30 minutes of idle time.
Regular polling checks for new mail at fixed intervals (e.g., every 5 minutes), regardless of whether new messages exist. IMAP IDLE maintains a persistent connection and receives instant notifications only when changes occur. This results in faster email delivery and lower resource usage.
Most modern email servers support IMAP IDLE, including Gmail, Outlook, Yahoo, and popular self-hosted solutions like Dovecot and Cyrus. You can check server capabilities by looking for IDLE in the CAPABILITY response. Some older or basic IMAP servers may not support it.
Delays can occur due to network issues, NAT timeouts disconnecting the IDLE session, server-side rate limiting, or your email client not properly reconnecting after connection drops. Mobile networks are particularly prone to silently dropping idle connections.
Standard IMAP IDLE only works on one folder at a time per connection. To monitor multiple folders, you need multiple concurrent connections. Some clients and servers limit the number of simultaneous IDLE connections, so prioritize your most important folders.
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