Mail App marks email as junk, over and over
How can I fix the Mail app so it doesn't mark legitimate email as junk?
This problem recurs across email I receive from a swath of my legitimate correspondents even after I have marked their mail as "not junk" over and over.
These senders are in my contacts, but some, not all, of their email is considered "junk" by the Mail app. It seems that just changing the classification of email from junk back to legitimate may work for a while, but within a couple of weeks, their email is right back in my junk folder. Sometimes these items include invoices, quotes, pictures, etc.
How can I get mail from a user to be allowed through iCloud/MacOSX mail servers without it being classified as junk?
MacBook Pro 17" Core Duo, Mac OS X (10.5.8)