Undeliverable local mail: how do I change postfix behaviour to bounce message?

[Simone Ruffilli]

Is there a way to disable address checking (both local user existance 
and RFC compliance) before accepting an outgoing email?

Whenever I try to send a mail that includes a non-existant local user in 
the recipient list the server immediatly complain a 5.1.1.

I'd like to change that behaviour making so that postfix accepts the 
email and then return me an undeliverable notice.
I'd prefer to receive a bounce than being blocked from sending a mail.

Thank you