DriveHQ has recently implemented a very powerful spam filter. All incoming emails are filtered globally. Most of un-trusted IP addresses, esp. those dynamic IP addresses are blocked from sending emails to DriveHQ. Based on a set of sophisticated criteria, emails are rated with a spam score and tagged with [Spam *] ... [Spam ****], with [Spam ****] means highest probability of a spam email.
To automatically filter spam emails, you need to use an email client that supports "email rules", such as Outlook and Outlook Express. You can add a rule to your Outlook to automatically move emails with subject line tagged with [Spam...] to the junk mail folder.