how to list catch-all ?

[ML]

I wonder how to know if a mail is catched by the default alias.
What i'm trying to achieve is to add a rule in my antispam when the  
mail is sent to a unknown address

I have such lines in virtual_alias_maps :

@vitualdomain1.tld      [EMAIL PROTECTED]
@virtualdomain2.tld     @virtualdomain1.tld
[EMAIL PROTECTED]       [EMAIL PROTECTED]
[EMAIL PROTECTED]       [EMAIL PROTECTED]
[EMAIL PROTECTED]       [EMAIL PROTECTED]

I want to log (or prepend i.e. X-CatchAll: yes) recipients (smtp  
level) of mails passing through lines 1 and 2 and no other. In other  
words this mean any rewrite made using an entry starting with @

Thanks for any advice...