[exim] Detect spam by cheking subject

Hi!

I saw many spamm messages have same subject.
How can I use this for spam filtering?
For example, after "mail -f mailbox" I see:

 N149 audrey@???  Tue Mar 07 16:51 105/4041  
"=?windows-1251?B?y+Dt9+gg5+Ag7eDs6CE=?="
 N150 dug-kyoo@guadalupano  Tue Mar 07 16:54 105/4070  
"=?windows-1251?B?y+Dt9+gg5+Ag7eDs6CE=?="
 N151 debra@???        Tue Mar 07 16:55 105/3989  
"=?windows-1251?B?y+Dt9+gg5+Ag7eDs6CE=?="
 N152 ashok@???      Tue Mar 07 16:57 105/4043  
"=?windows-1251?B?y+Dt9+gg5+Ag7eDs6CE=?="
 N153 fu-zong@???     Tue Mar 07 17:02 105/4021  
"=?windows-1251?B?y+Dt9+gg5+Ag7eDs6CE=?="

Really, this is spam.
How can I cut subject, save it in somewhere and in future, use it for
check other messages?

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With best wishes
Victor Vislobokov