I Wish the Framework Team Used Interfaces More

One of the things that often bugs me about the .NET Framework is that so many of the classes are written without an interface. A case in point is the System.Net.Mail.SmtpClient class. This is an excellent class and very useful. It extends System.Object, but it does not implement an interface. This is extremely frustrating!It's not that I would like to write my own version and swap it in, but I