Multiple Domains & Sendmail

Chris Gill asks: "I'm trying to setup Sendmail to handle multiple domains. I have three domains that it needs to receive and send as. Is there a way to map names into each domain, and have Sendmail change itself depending on who is sending the mail? (So that bob@domain1.org and dave@domain2.org can be sent from the same machine, with return addreses in their correct domains.) "