mail server issues

I am running Caldera 2.3. I have sendmail installed and running. The problem is that when I send mail to somebody on the local network, it acts like the mail was sent properly but the individual may or may not get the mail. If I attempt to send myself something through Outlook 2000, it appears to send it, no errors, but when I check my email, there is nothing there. How can I tell where the email is going and how can I change the location users mailboxes?

Brian