How to write vendor SPAM filter?

[Siegfried Heintze]

I have a prospective client that wants me to write a vender neutral spam filter.
How does JavaMail work? Is it only a client API?
Java seems like a great candidate for vendor neutrality. Are there any open source POP3 servers each user could run in the back ground that would periodically connect to the ISP's POP3 server and filter messages? I could modify the pop3 server to implement a SPAM filter. Then the user would point Eudora or Outlook or rmail at the local POP3 filter that has filtered everything.
Siegfried

[Stan James]

I use a proxy spam filter with Eudora. I point Eudora to get mail from a local port which is the proxy. It forwards the requests to the real mail server and analyses what it gets back. Now that I'm trying to explain it, I realize I don't know just how that works! That might be a desktop solution that could work with multiple mail clients.