Make sure it's enabled for Users: Domain Settings > Advanced Settings > Default User Settings. Ensure "Enable IMAP Retrieval" is checked.
Then make sure it's enabled for an individual user: Domain Settings > Users. Select the User, then on the User tab, the same setting should be checked: "Enable IMAP Retrieval"
You may have to log out and log back in to see the item show up under Advanced Settings.
Derek Curtis
COO
SmarterTools Inc.
(877) 357-6278
www.smartertools.com