Microsoft CDONTS Provided as part of IIS 4.0 or later. Also known as the Microsoft SMTP service in IIS. There are actually two parts to this. The part that ASP scripts use is a COM component that allows your script to work with email. All the XCENT scripts use the CDONTS.NewMail object. The second part is actually a SMTP server. This part works just like any SMTP server software. It is a very basic SMTP server and does not have any good management tools. However, it does a very good job of sending email from within your ASP scripts. It can be configured to run with another SMTP package either on the same or different server. Because it queues up messages for delivery, it is very robust and efficient, even on busy servers.
Pros: Free component of IIS, efficient.
Cons: Lack of comprehensive documentation makes many wary of using it.
Alentus does not offer the usage of CDONTS on its ASP only servers; however, it can be used on Asp.Net applications. Please see related article in knowledge base.