Masquerade sender's domain from sendmail

["Brad Alpert" <BAlpert@xxxxxxxxxxxxxxxx>]

Probably this is the impossible dream, but..

I have a couple of different domains on my internet RH 9 server.  I
would like to learn how to specify how to make email appear to come
from particular domains based upon the sender's identity.

Can this be done using webmin?  I am not using M4 because I haven't
synchronized an M4 configuration with the sendmail.cf configuration
which I built using webmin.

Any tips appreciated.

Thanks/Brad