Drupal allows you to substitute in your own mail backend. You can write your own backend that sends direct SMTP requests to your company mail server.
Note: I have never attempted to do so myself, so I have no idea how much work it is. :-) I know the devel module does offer that functionality, so I suggest looking at the devel module and at the drupal_mail() function to see how it works. I'm afraid I can't offer more detailed advice than that.
On Wednesday 26 March 2008, Tony Yarusso wrote:
The guy who maintains our network with me is concerned about having open mail ports in the firewall for web (http) servers. Therefore, we would rather have one dedicated mail server machine that would handle everything, rather than letting things like Drupal mail out via PHP. How would I go about setting up Drupal to delegate / relay this task through another server?