ok dude here goes:
Sendmail is an smtp server... it is used for receiving and sending mail...
Now sendmail is by default setup to start automatically with the following settings:
Service is NOT receiving mail from the internet
Service is ONLY sending mail from the local machine
SMTP runs on port 25 by default, so you can access it by typing "telnet localhost 25" in console
(That was to help you understand what it is)
Now.... the problem you're having is with your recieved mail directory... mybe it doesn't exist?... anyways.. heres how mines setup...
owner = root (all permissions)
group = mail (all permissions)
other = all but write
* non recursive
same as above
Your error message tells me that the permissions for your send mail directories are wrong, this can probably be fixed by simply uninstalling and installing sendmail from your redhat cds
I've just started using linux sendmail so I could be wrong