Spam Block Advice

Hello,

A couple days my client complain about receiving a SPAM mails.

Ive check the massages headers and most the Spam Score its around

X-Spam-Score: -21
X-Spam-Score: -41
X-Spam-Score: -6

I would be glad for useful guidelines to stop unnecessary spam

Keep in mind that my exim4 conf the score it`s setup to 25 and still the spam comes