Many email clients offer the ability to use the IDLE function of IMAP. What the IMAP IDLE function does is leaves a connection open to the mail server so that when new email arrives it immediately alerts your mail client and pushes the new message to you.

This is a very good thing to have configured for your mailbox, in theory, however in practice the way that Apple’s Mac Mail handles this function of the IMAP protocol it leaves multiple IMAP connections open instead of just one. Over time these can pile up, diminishing available resources on both your computer and the mail server. This can result in both Mac Mail and your entire computer being sluggishly slow, or even being blocked from connecting to your mail server for a DoS (Denial of Service) attack.

If you are using Apple’s Mac Mail you might want to disable this specific function. To disable IMAP IDLE in Mac Mail follow the instructions below:

1. From the Mac Mail program click on the MAIL menu and choose PREFERENCES.
2. Click on ACCOUNTS.
3. Select your IMAP account from the list in the left-hand pane.
4. Click on the ADVANCED tab.
5. Disable the “Use Idle” setting.

When the IMAP IDLE command is disabled your Mac Mail will continue to retrieve new email messages at regular intervals defined in your Mac Mail Preferences. For information on how to change how frequently Mac Mail checks for new messages see How to change how often Mac Mail checks for new messages.

Posted in: Email