Electronic mail software includes a main email component and a number of installable components which communicate bidirectionally with the email component through an application programming interface (API). The installable components include authoring/reading components and a mailbox browser/editor component. The main email component provides an underlying graphical user interface (GUI) for functions directly associated with the storage and transfer of electronic mail messages and also handles all data bundling and unbundling that may be required to transform a message created by an authoring component into a fully MIME compliant message. In addition, the main email component includes "hooks" (an application programming interface or API) for the attachment of the installable components. The authoring/reading components each provide functionality particular to the type of document the component is designed to create/display. Some modular components, or messages created by them, have assigned "roles" whereby senders and recipients of certain email documents are provided different kinds of access to the documents.