If you are using a Windows 2000 / 2003 Server, or even XP Pro chances are that CDOSYS is your best bet for sending email from Active Server Pages. That is because CDOSYS is installed on all of them by default. Gone are the days of using CDONTS which was the old way of sending email from ASP. CDOSYS is it's replacement.
That being said there are actually a lot of ways to configure and use CDOSYS. When I 1st started using CDOSYS I assumed the CDOSYS code I was using would work in any situation, but that is not the case. This is something most articles about CDOSYS do not mention so I am going to show you 3 different CDOSYS examples each sending email using a slightly different method.
Method 1 involves sending email using a local pickup directory. Meaning you have the IIS SMTP Virtual Server Running. If you are on a local development machine this is probably for you. Under this scenario any emails you send from your scripts put a ".eml" file in the local pickup directory. Then hopefully the SMTP Virtual Server grabs the file and sends it off. The Virtual SMTP server is however known to hiccup and not send out the emails right away.
Method 2 involves port forwarding. I am not exactly sure how you set that up on the server but the code I wrote for it works under that scenario. The hosting company known as Verio actually implements this with CDOSYS on their servers. I actually implemented this method in some of my software because of a customer that couldn't get emails to send on one of their servers.
Method 3 involves sending the email using a remote mail server. This supports outgoing SMTP authentication should your server require that for outgoing emails. Many do these days. This method is also the best method to use because you are using a real email server with valid MX records. Many modern email systems block emails that do not have valid MX records and you want your emails to reach the recipients.