Let me start by saying I am not a sendmail expert and this will not tell
how to secure sendmail. This is only how to make it work.
Once you get it working then you can tighten it down.
This is what a typical sendmail.mc
looks like. This is modifed to fit more things.
Again, this is not a secure file just one to start with.
Once you have the file you want look at the top of the file you will notice
the m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
you'll have to run that
command each time you modiy the sendmail.mc record. You can also edit the
/etc/sendmail.cf by hand, which I tend to do once I run the "m4" command.
any everything is still ok.
The access file is the file where you need to put hosts that can use you system for mail.
Most of the info for that is here
local-host-names is just name. Names that your system will present and recieve for.