special exim configuration

[ujr@physik.phy.tu-dresden.de (Ulf Jaenicke-Roessler)]

Hi,

 is it possible to configure exim such that outgoing mails
 appear to come from another host *and* mails between local
 users really come from the local host?

 My current configuration "masquerades" *all* mails as coming
 from another host. This is bad for replys, especially if the
 sender is root, because replys would go to a similar account
 (e.g. root) on the wrong host.

 Thanks,

  Ulf