CDOSYS is a Windows component which is used to send email by SMTP - similar to its .NET successor System.Net.Mail. Both of these APIs have their own strengths. Some developers don't want to use CDOSYS since they want to stick with an all .NET solution. However, CDOSYS is pretty seasoned is very capable and is viable for even new programs. You should always target your releases to a specific platform (x86, x64, etc) when using COM objects and likewise be calling ReleaseComObject on those objects to prevent leaks. There are not many good examples though on using CDOSYS which show how to use it properly and exercise its capabilities, so I have been working on one and have published an initial BETA of it on Codeplex. Right now its BETA, so I have more work to do on it. In the mean time please check it out if your looking for a sample or something to do basic testing in a lab.
This is another sample I wrote which uses CDOSYS. It shows how to use CDOSYS to load a message's MIME and parse it. It can extract properties and export content from the loaded MIME.
CDOSYS MIME Parser
This is a similar SMTP mail sender which uses System.Net.Mail and was written by a fellow team member:
NetMail Sender Tool using System.Net.Mail