The local-host-names contain your local domain name what is not forwarded anywhere else. Eg.: local mail communication and internet communication on the same box.
The mailertable contain the forwarded domains. Eg.: The emails come from internet into linux box then filtered spams then go to local Exchange server or another local sendmail box.
The virtusertable contain the multiple domain / multiple user configuration. I think this is for you.
Or you can forward with .forward file too.
If you use the .forward file you have to put this into sendmail.mc file.:
Or another possibility to forward mails to different account is the aliases file.
info-list: chris, tweeks, email@example.com
It means the firstname.lastname@example.org
will be delivered to all that accounts. (the domain.com is in the local-host-name file)
I hope it helped.