Blocking Email Addresses

Are you by chance trying to use the block senders feature to control spam?  If so this technique isn't really that effective unfortunately because it blocks based on the sender's email address which in the case with spam is almost always falsified so as to circumvent blocks such as this.  Spam filters look at all aspects of the message to determine if it is considered spam in nature and using the report as spam feature helps to further train the filter to recognize new messages.