MerpsMom,
Filtering to allow only emails from those on your mailing list, as you say, excludes Grumblers who are contacting you for the first time. And a list of blocked senders does not work for the pro spammers, since they change small details of their email address with each mailing. You may block
ertw2563@spam.net only to get the same junk from
ertw2564@spam.net the next day.
There are utilities, some of them free downloads, that allow you to block messages containing certain key words or phrases in the subject line. I haven't investigated these thoroughly, since I use Hotmail, which has this utility built-in. I have 25 custom filters set up that block messages containing words like 'adult', 'mortgage', 'debt.' The bonus is that, if I get a message with a subject line like, "Why can't you act like an adult on The Grumble?" it will be blocked!
This strategy has been so effective that my spam has been reduced in a few weeks from several dozen each day to about one each day.
Today I received three messages that were not blocked but ended up in my junk folder for examination. Two contained viruses and the third contained an offer for a new virus checker. My Norton Antivirus is always on full alert and my virus definitions were only 3 days old, so it appears I'm okay. I ran a full virus scan and the system is clean.
BTW, Hotmail did not catch these viruses. They were picked up by Norton's in Outlook Express, which I often use even for my Hotmail account.
I'll do some checking on the filtering systems available and post my findings here.