With IMAP accounts, Mac OS X Mail can use the IDLE command (provided the account supports it). Instead of periodically polling the server for new mail, Mac OS X Mail only waits for incoming messages, which are sent automatically and appear almost instantly.
Get instant email updates with IMAP IDLE in Mac OS X Mail
To have emails appear instantly in Mac OS X Mail IMAP accounts:
- Select Mail | Preferences… in the menu.
- Select Accounts .
- Select the desired IMAP account.
- Go to the Advanced tab .
- Make sure that Use the IDLE command if the server supports it is checked.
- You can additionally uncheck Include when automatically checking for the existence of a new mail . Note, however, that Mac OS X Mail only receives instant updates for the open folder.
- Close the preferences window.
In Mac OS X Mail 2, you can use the IMAP IDLE plugin.