how can I get the final address which postfix sends to for local addresses?

[slan...@googlemail.com]

Postfix can use alias files and other means to rewrite an address.
How can I find out what the final address for local addresses will be?

Let's say I a going to send a mail to webmaster without specifying the @.. part.
In this case I think postfix uses localhost as default and eventually looks for an alias in /etc/aliases for example.
There it may find that webmaster is aliased to root and in turn it may find that root is aliased to myadm...@mymailprovider.com.
So the final address postfix sends to is myadm...@mymailprovider.com
Is there a tool to get this final address?

I can of course just send a mail and look at the mail.log but that is no real solution.