Setting up sendmail

Hello again, I'm trying to setup sendmail on my dyndns address so that people in my company might use it as a smtp server. Is this possible with crux? How do I open up for externally use, possibly requiring some authentication to avoid misuse. I know this doesn't have directly with the crux kernel to do, but maybe you could point me to some "newbie" docs on this, I found the document http://www.sendmail.org/doc/sendmail-current/doc/op/op.pdf, but the document were just overwhelming... Helge