Logging only undeliverable messages?

[Joshua Pollak]

Hello,

I've made the modification to qmail to log all messages, however, I was 
wondering if there is a way to modify that system so that only locally 
undeliverable messages get stored? I don't really want every message 
logged, but if a message comes in for a user that qmail can't find, I'd 
like to log that message.

Is that possible?