Outlook's Architecture

When you are troubleshooting Outlook connectivity issues, you may heard a lot of items, such as MAPI, RPC, etc. If you ever wonder what they are and how they fit together to make Outlook connectivity possible, you need to have a understanding of Outlook's architecture.

In General, there are several layers when it comes to Outlook connecting to a messaging system (like Exchange):

• Outlook
• MAPI Layer
• Service Provider Layer
• Transport Provider
• IP/Ethernet Layer

The interfaces between layers are COM interfaces. Each layer exposes one or more COM interfaces as well as methods on these interfaces.

For Outlook connectivity to work, each layer needs to function as expected. I made a figure  and hope that it helps with understanding of these layers.