Rewriting email addresses

[Daniel L. Miller]

Is it possible to:

1.  Rewrite the sender based on the destination?  Particular example - 
using a fax-to-email service, only one email address is allowed to be 
used.  So I want any message addressed TO "xxxxxxx...@faxpeople.com" to 
be sent FROM "designatedu...@mydomain.com" (from a valid client, of course).

2.  Rewrite the destination based on the sender.  The reverse case - a 
received fax image is returned, but instead of going to the original 
recipient, rewrite the recipient to "f...@mydomain.com" when the sender 
is "nore...@faxpeople.com" so my auto-print service will do its job.

Can this be done using Postfix's built-in rewriting?  Or do I need 
something external?

--
Daniel