User unknown detection

[Pietro Romanazzi (detto Massimo)]

Hi guys,
it seems that the “User Unknown” detection is taken in the smtp-protocol so the 
mail with one unkown user will never arrive to any processor (it is rejected at 
smtp level).
Did I understand it well? Is there any way to bypass this smtp check and manage 
the mail in custom mailets?
I need to produce specific logs and receipts even for mail with unknown user.
Kind regards,
Pietro