yeh its possible ...... iam not sure about the exact way ....
1.check out the function of the /etc/sendmail.cw file.
2.the virtusertable feature does exactly what u want to. However sendmail must be compiled to do this ... u can use m4 however.
There is this concept of virtual domains ..... read the FAQ on www.sendmail.org
for more details.
Here iam pasting some text i found on the NET :
The virtusertable & virtusertable.db files
A virtusertable is a database that maps virtual domains into news addresses. With this feature, mail for virtual domain on your network can be delivered to local, remote, or a single user address.
The domaintable & domaintable.db files
A domaintable is a database that maps old domain to a new one. With this feature, multiple domain names on your network can be rewritten from the old domain to the new.
Hope this helps.