I do pay a small fee for it, but "SpamArrest" was suggested to me - and it works fine.
SpamArrest checks your servers inbox, checks all the addresses (set up was absolutely painless - though I've forgotten what) and then sorts out good mail into its own inbox and potential garbage into its own junkmail box.
You set your own e-mail client to download from your spamarrest account - NOT from your ISP.
You can, of course, go and glance at you junk box any time you wish and decide if any of the incoming junk is actually good stuff.
Anybody writing to you for the first time after you set up will receive an automated reply asking them to verify - if it's a good address, they will get the reply - if it's a garbage address, they won't.
Adding, blocking, deleting addresses all comes very easily.
Not surprisingly -
www.spamarrest.com