I don't know if this is right. Just new in using gmail.
You can start by setting up spam_filters for certain messages TO, CC, From, etc...message headers to avoid most of spammer mass mailing dictionary trix; as well as checking the Report_Spam Box before deleting the messages to help the Googler Team with thier research on these INet menaces. You can also have your Gmail spam folder dump at set intervals. See; Help + Settings.