failed to sending emails on helpdesk and newsletters, pls tell me how to fix it.

server win2003 + apache2.2+php5.3.5+mysql. is anything I missed? I use it all well in a shared host but why on my vps it is failed.

Did you configure the e-mail sender address in the Lms?

If yes, are you sure your server is configured to allow sending e-mails from an application, such as an LMS, and has the necessary services turned on?