System.Web.Mail is simply a wrapper around the two COM libraries: CDONTS.NewMail (found in the cdonts.dll) and CDO.Message (found in the cdosys.dll). You will also need them installed on your server. By default cdonts.dll and cdosys.dll will be installed in WindowsNT/2000/XP/2003.

What’s more, if you trace into the class System.Web.Mail.SmtpMail, you can find some odd behaviors:

• It only supports Win32NT operation systems, for example, windows 2000, windows 2003, windows XP.
• When the SmtpMail class sends the MailMesage, the SmtpMail class checks the OS version. If the version is <= 4, CDONTS.Newmail object is used and for all operating systems greater than 4, CDO.Message object is used.

Because of these conditions, your troubleshooting will become much more difficult, when moving the code to different OS’s. And your application may get unexpected results from different OS.

Aspose.Network.Mail is a .Net component written in fully managed code in pure C#. It has Zero reliance on any COM libraries, including CDONTS.NewMail, or CDO.Message. Therefore, with the help of Aspose.Network.Mail, you can avoid invoking any unmanaged code in your applications, increasing reliability and free of boring COM debugging. Aspose.Network.Mail is rich of feature and provides much more services than those provided by System.Web.Mail architect.

System.Net.Mail is a new SMTP protocol client implementation in .NET 2.0. It is also a pure managed code implementation in C#. However, System.Net.Mail only provides simple email sending functionality and does not support .NET 1.1

Here is the Matrix: