Good Spam Filter service?

I need to be able to point the MX records for my domain(s) to say, a spam intervention service, have them filter out any spam, and then have the legit mail forward to me from them.

Unfortunately I can’t implement anything with my mail server, so this is how it must be.

I’m using Lotus Domino 7 for mail.

Blacklists and checking for legit reverse DNS entries aren’t good enough these days :frowning:

If anyone has any good suggestions please let me know!

Thanks in advance.