EMAIL from web server

Question

We have a website sending mail alerts to end users. The site has been developed in c# ASP.NET.

I want to find the best way to send the email alerts to my users. Making sure the mail is not trapped in any spam filters. I read on the internet it is best to sent the mail directly from the web server and not route via an SMTP mail service such as google apps or Postini.

Can anyone tell me if this is correct?