Hawk Internet Services spam filtering device uses two rule sets: UCE/Spam and Explicit Content.  For each rule set, both the header of the email message and the body of the message are analyzed.  The header is the part of the email that tells your email reader who sent the message, when it was sent, who to reply to, what attachments are included, the message's format, and more. We regret that we are unable to make the filtering criteria available on this site because we know many users are interested in seeing why certain messages were blocked. However, if we were to make our filter lists available to the public internet, spammers would use our own tools against us to get around the rules. This type of filtering is a constantly evolving service. As new spam is reported, new rules will be added to detect and quarantine it. Likewise, as legitimate email is reported as having been quarantined, new rules will be added to allow it through.