Web-Based Emailers That Allow an Access List?

claud9999 asks: "Are there any web-based e-mail services that would limit receiving e-mail from a list of specified addresses (bouncing all other e-mails that aren't from that list)? At first I thought someone like Yahoo would filter SPAM simply as a matter of managing liability and space consumption but they almost seem to encourage spammers as my yahoo account generates the bulk of the spam that I receive." It seems like this would be a fairly easy thing to implement, I mean, how difficult would it be to stick a web interface in front of procmail? Does your e-mail web-based service do this? Maybe it's time to start sending some polite emails encouraging them to do so, if they aren't.