[Dovecot] inform users's about new spam

[ckubu]

Hallo evryone!

Mailsetup: postfix+dovecot2 with postgres database backend - about 2,000 
virtual mailboxes, growing..
New possible spam will be sorted into a users directory named "spam", emails 
older than 30 day's in that folder will be deleted by using expunge.

I would like to inform my users evry two day's (or something like that)  about 
new emails in the spam folder. Can you give me a hint how to handle that ?

Are there helpful tools , or have i to wrote my own script, walking through 
the folders, checking for new emails since last check and finally inform the 
user if needed.

Best wishes
Christoph