Over the past few weeks many customers have been experiencing issues with the spam detection accuracy. After some research by our engineers, the problem occurred because SpamAssassin was calculating the date of the emails incorrectly, which threw almost all emails into a "Spam" status. We have applied a patch which fixes this issue so spam detection should be working normal again.
Since some of our customers were deleting suspected spam messages on the server (a setting in your control panel) most emails were being deleted. We always suggest that you de-select this feature and setup a rule in Outlook that moves spam messages to a different folder. You can do this since all spam messages will have "****SPAM***" in the subject line. This way you can always review the emails before they are deleted.