Like there is not enough sendmail information on the net here is a quick and dirty tip for you.
Want to send one email to multiple receipients/users using sendmail here is how.Edit the virtusertable file and add the user and the alias where the email will go to. The alias is a group name.
vi /etc/mail/virtusertable firstname.lastname@example.org DM-group
Save and close the file, and now make the file
cd /etc/mail make
Now it is time to add your aliases, but before you do that make sure that you sendmail.mc file has the correct location for the aliases file.
If you made any changes to the sendmail.mc file then you must change the cf file. You do that with the following command.
m4 sendmail.mc > sendmail.cf
Now make or edit the aliases file in whatever location you specified in the sendmail.mc file. I use the /etc/mail/ folder for all my sendmail files.
vi /etc/mailaliases DM-group: email@example.com, firstname.lastname@example.org
I added two recepients in my DM-group, now you have to map the aliases.
And presto all you need to do is restart sendmail
/etc/rc.d/init.d/sendmail stop /etc/rc.d/init.d/sendmail start