The following figure shows the high-level component relationships in the Messaging Architecture. Dashed boxes indicate components that can be developed by third-parties.

- Messaging Architecture Overview
The following list summarises the components. The remainder of this topic explains each of them in detail.
- Application/App UI: This represents a message client application, such as ER5s Email.
- User Interface MTM, Client-side MTM, UI Data MTM, Server-side MTM Libraries: These libraries provide base classes required for implementing protocol-specific MTM components. They also provide registry classes that allow MTM components to be located and loaded.
- Concrete User Interface MTM, Concrete Client-side MTM, Concrete UI Data MTM, Concrete Server-side MTM: These represent instances of MTM components written to implement a particular messaging protocol. User Interface and UI Data MTMs handle user interface functionality and resources. Client-side MTMs provide message data handling functions. Server-side MTMs provide message transport functions.
- Message Server: The Message Server handles all requests to access or manipulate message data. Where necessary, it passes requests to protocol-specific message transport components, known as Server-side MTMs.
- Session Library: Sessions allow client-side components to issue requests to the Message Server. The same library provides a class to clients that encapsulates an individual message entry.
- MENT: to simplify the figure, this library is not shown. It provides utility classes for accessing message data, and is used by all other components.
Note that no lower-level communication components are shown, as the Messaging Architecture is designed to be independent of any particular communication protocol. Instead, communications libraries are accessed as needed by Server-side MTMs. In ER5, the SMTP and POP3 MTMs use TCP/IP, while the SMS and Fax MTMs use the EPOC Telephony Server (ETel).