Quotient uses the very popular SpamBayes package to categorize and filter out spam. (from the spambayes website)
SpamBayes will attempt to classify incoming email messages as 'spam', 'ham' (good, non-spam email) or 'unsure'. This means you can have spam or unsure messages automatically filed away in a different mail folder, where it won't interrupt your email reading. First SpamBayes must be trained by each user to identify spam and ham. Essentially, you show SpamBayes a pile of email that you like (ham) and a pile you don't like (spam). SpamBayes will then analyze the piles for clues as to what makes the spam and ham different. For example; different words, differences in the mailer headers and content style. The system then uses these clues to examine new messages.
You can go here to read more about how Quotient integrates SpamBayes into our total spam-filtering solution
So, having given you all the background information, this is where quotient puts messages that our filtering system has determined (according to your rules and classification) is most likely to be spam. If you find a message in this folder has been been falsely classified as spam, you can simply move the message out of this folder into its proper place, and it will automatically train the message as 'not-spam'.