SPAM filter problems

Question

All of a sudden, I'm getting tons of SPAM. It is coming on both my ISP mail account and my .mac account. I have set my preferences to filter all mail where the sender is not in my address book. I receive it anyway.
What's even more frustrating is that some mail where the sender IS in my address book (my daughter!) is being marked as SPAM by my filters. Huh?
I have tried checking the "trust my ISP" box and then I wasn't receiving about half my mail so I have now unchecked that box.
Any ideas?

Answer 1

Sounds like you have become the victim of what is called a dictionary attack by a spammer or spammers who use an automated program that guesses at email addresses with a particular domain.
The default junk mail rules under the Advanced tab are set up as follows:
If ALL of the following conditions are met:
Sender is not in my Address Book
Sender is not in my Previous Recipients
Message is not addresses to my Full Name
(and if) Message is Junk Mail - determined by the junk mail filter's "learned" settings by you marking a message as junk or not junk,
Move message to mailbox Junk.
Even if you have filter all mail where the sender is not in your Address Book, the message must still go thru the filter which does not mean the message will be automatically marked as junk.
Since your daughter's email address should be exempt from any junk mail filtering, something is wrong so I suggest doing the following first.
Go to Mail > Preferences > Junk Mail and disable Junk Mail filtering.
Quit and re-launch the Mail.app and re-enable Junk Mail filtering.
IMO, I wouldn't adjust, add to or remove any of the default Junk Mail rules via the Advanced selection and allow the filter to do its thing. If disabling and re-enabling the Junk Mail filter does not resolve the problem, I suggest using the Reset feature which will reset the Junk Mail "learned" settings and you can keep Junk Mail set to automatic when doing so.
Regarding having problems with "Trust junk mail headers set by my ISP" selected, this indicates the spam filter at your ISP's incoming mail server is marking these received messages as spam which is called a false positive since the messages are valid.
I've never experienced any problems having this selected but if a valid message is marked as junk when received because of this, marking the message as Not Junk and moving it from the account's Junk Mailbox to the account's Inbox mailbox should prevent this from occurring again but it make take several "Not Junk" processes to "train" the filter.