catchall in postfix

[Sven Verluyten]

Is it possible to configure the postfix part of kolab in such way that 
if a mail is sent thru kolab's smtp and the recipient is NOT a local user/list
and is NOT in the postfix/transport table, to then, and ONLY then
forward that email to a specific server ?

I tried making suck catchalls for @domain.tld in virtual, transport & aliases 
without result

Thx in advance for some help

Sven,