[Dovecot] Proxy using passd file

I'm trying to create a proxy using passwd files. Can I use the existing passwd files created by the system (ie passwd and shadow) or do I have to create new passwd files for the email proxy users? How would the passwd and shadow files for a proxy using passwd files look? I've tried the example on the wiki but I'm not getting anywhere, pop and imap requests are not getting sent to the other server.