Spam filter

Hi,

Over the past few months, I've notice more and more spam coming to all users in my domain. Fortunately, the spam filter does a good job and catches most if not all the spam e-mails received by those users. However, it has also been catching many legitimate emails. I have been forced now to sift through all spam emails every week to make sure that there aren't legitimate ones being filtered out. When I find a good e-mail, I mark them as Not Spam to get them back. However, I still notice that the following weeks, e-mail from that same sender and being sent back to the Spam folder. This is happening to many e-mail senders, not just to one and whitelisting every single sender is both time consuming and not feasible in the long run as I cannot predict new future senders. Can you please advise.

Thank you.
G