Wanted email server assistance & advice

Time Warner is my broadband provider, I have 8 email accounts there. I am using ‘Janaserver’ as an email server, it collects pop3 mail and sends smtp mail for my local users. I wish/need to be able to filter inbound (pop3 from time warner) mail by sender, what I really wish to do is limit whom my local users can receive mail from. I am not married to ‘janaserver’ so I am willing to try pretty much anything. Like I stated above my internet email is hosted at Time Warners email servers, so I need to collect POP3 from Time Warner, store them on my local server for retrieval by the local users. Yes my local mail server is physically between my users and the internet so it is providing Web Proxy services also.