OT: mail server

This is actually off topic, but I can bring it on topic if I do this right (see further on). My mail server's hard drive has developed bad blocks. I could fix it, or I could take this as the sign that I need to get off my butt and move to a more advanced product. I'm currently running SIMS on an old Mac (eh eh, on topic!). But it lacks a key feature that I want... content filtering so I can block certain kinds of email. What do others recommend as a decent mail server that can handle content filtering, multiple domains, POP access, and is free or darn near it. And for the on topic nudge, I would like to be able to run it either on an old Mac (probably not possible), or on mac68k NetBSD (so I can still use my old Macs). Although I am not hard core on platform or OS, that's just a "I'd like" option. A web mail component would also be a nice thing if available. I'm looking into Postfix or qmail, but I've only just started the research, so I figured I'd see what others are using or recommend. -chris <http://www.mythtech.net>