Since you are using vhosts, aliases won't quite do the trick. You'll have to use virtusertable instead. Create a text file like the following:
info@domain1.com user@domain1.com
webmaster@domain1.com user@domain1.com
info@domain2.com user@domain2.com
webmaster@domain2.com user@domain2.com
If you want ALL mail for domain2.com to go to a user at domain2.com, you would just leave out the name in the For column:
@domain2.com user@domain2.com
once you have this file created, name it virtusertable and runn the following command:
hash /etc/mail/virtusertable
This will create /ete/mail/virtusertable.db
You may have to restart sendmail to read the new file.
If you still haven't gotten relaying to work. Create a file called /etc/mail/access and add these lines:
domain1.com RELAY
domain2.com RELAY
then run this command:
makemap hash /etc/mail/access < /etc/mail/access
This will create /etc/mail/access.db
Hope this gets you up and running.