Yes. SPAM filtering is enabled for all accounts by default and marks the subject of emails with SPAM-LOW, SPAM-MED or SPAM-HIGH if the filter believes the email to be SPAM.
Configuration settings for the SPAM filter can be adjusted on a mailbox by mailbox basis. To change your SPAM filter settings please log into the webmail facility for your mailbox and select 'My Spam Filtering' from the settings menu.
We also use Greylisting to reduce Spam. Please see the knowledge base article titled 'What is Greylisting?' for more information.