CDO & MAPI Programming with Visual Basic:

Appendix A. Programming Internet Email Protocols

This book is primarily about Messaging Application Programming Interface (MAPI)—Microsoft’s abstract interface to messaging systems. Throughout the book, you’ve seen that programming against MAPI allows the intricacies and peculiarities of specific storage and transport mechanisms to be hidden behind MAPI service providers. This is a powerful architecture that simplifies messaging application development. Without any knowledge of Internet protocols, for example, client applications can send and receive email via the Internet.

However, there is cost associated with this power. The computers on which MAPI client applications are to run must have MAPI installed on them, and they must have appropriate MAPI profiles set up. In addition, most of the code in this book requires CDO to be installed. If you have an application in which for some reason you do not wish to use MAPI, you might consider programming the Internet protocols directly. This appendix shows you how to do that using the Winsock custom control that is included with Visual Basic 6. (If you’re writing an application to run under Windows 2000, you can use CDO for Windows 2000 instead. See Chapter 12, for details.) Be aware that when you choose not to use MAPI, your application becomes intricately tied to the underlying storage and transport mechanisms, making it very expensive to add support for different storage and transport mechanisms in the future.

How Email Is Sent on ...