Maybe there is a better way of doing this.
I have SELinux Fedora 8

The only function of this machine is to upload files to its FTP and send e-mail to the intended recipient and sender that the files are ready for download. I am using a simple yousendit.com clone script that just does that, uploads the file, sends and e-mail and the recipient gets a link to download it. We set it up to only accept upload requests from inside our network.

My upload form ask user to browse for the file add message and e-mail of intended recipient. after they hit send the file gets uploaded and an e-mail sent to the person to download it. I was using send mail to handle the e-mails but, recently our domain was blacklisted because the e-mails we were sending with this machine did not have the correct headers.

I don't know if it is easier to set up sendmail to use one of our pop accounts? This machine has no other purpose but to serve as a file repository.

Any help will be greatly appreciated.

If I understand correctly, sendmail can be configured through the SMART_HOST feature to use an existing smtp server to route all outgoing mail. define(`SMART_HOST',`[your.mail.server]') is probably what you are looking for. The brackets keep sendmail from doing a MX lookup through DNS.