Cornell's central email delivery service uses filters from Sophos to block or rate spam. The filters get better with real-world samples submitted by us. Here's a link to the page explaining how to do so.
How to submit spam, and false-positive spam samples to SophosLabs
http://www.sophos.com/en-us/support/knowledgebase/23113.aspx
Learn more from CIT about the PureMessage software from Sophos:
How to Identify Messages Labeled as Spam
http://www.it.cornell.edu/services/puremessage/spam-label.cfm