Net Nanny is not a spam filter. Net Nanny blocks words & phrases by "###" masking them out of e-mails (either Web mail, or Outlook POP3 clients). It can block senders by e-mail address; simply add the offending address to your Content Filtering list, eg:

bademail@bad.com*

In addition, if you're running Outlook, check the "Block Sender" feature which pre-emptively removes those persons emails from your Inbox. Spam-free web-addresses can be maintained by flipping on your "Junk Filter" in the Inbox, or registering with a site like www.spammotel.com Last, there are "spam free" products available to filter e-mail, try www.software4parents.com for more information.