If you have the anti virus software "avast!" installed on your system it will for some reason block connections from Unibox to the mail server. In order to prevent this first go to System Preferences and select "avast!".
Connection Timed Out (8099)
Then click on the lock to make changes. You will be asked for your Mac password.
Then click on the "Advanced"-Button for the "Mail Shield".
Remove the check mark from "Scan secured connections":
Click "Done" to save this change.