That is a very broad question.
Not very easily. Therefore, it is highly recommended that you don't publish your BB mail address anywhere, and only use it to forward mail from another account to it.
If you are getting too much spam/junk from your normal email address (POP email, via BIS), you should filter it at the server BEFORE the BB picks it up.
If you are getting too much spam on your
address, there are some suggestions about filtering your BIS account.
You can read this... http://www.blackberryforums.com/gene...BIS#post352375
or do a search of the forum using the keywords: spam filter BIS
and you will get several threads of info on the subject.