11. The computer-readable storage medium of claim 10 , wherein the preview handler calls an interface exposed by the electronic mail client application and receives a response from the electronic mail client application comprising an identity of a previewer for the document type of the attached document.
10. A computer-readable storage medium having computer-executable instructions stored thereon which, when executed by a computer, will cause the computer to expose a preview handler interface to an electronic mail client application, the preview handler interface to expose at least one method for initializing a preview handler and loading a previewer for generating a document preview, the preview handler to: receive a request from the electronic mail client application to generate a visual preview of an attached document of an electronic mail message; transmit a query including a file extension of the attached document to the electronic mail client application in response to the request; receive a response to the request from the electronic mail client application; identify a previewer for the document type of the attached document for generating the visual preview of the attached document from a plurality of separately executable previewers based on the response to the query provided by the electronic mail client application, wherein: each previewer of the plurality of previewers is separately executable from each other previewer and is registered with the preview handler as a previewer for previewing documents of a particular document type, and the plurality of previewers includes at least one of a word processor application program and a spreadsheet application program that is registered with the preview handler as a previewer for previewing documents of the document type of the attached document, capable of providing the visual preview of the attached document, and capable of being launched by the electronic mail client application for editing the attached document; load the word processor application or the spreadsheet application as the previewer for the document type of the attached document for providing the visual preview of the attached document, wherein the word processor application or the spreadsheet application is designated by the electronic mail client application as a loaded previewer for generating visual previews of other documents of the document type of the attached document when loaded; and transmit a request to the loaded previewer instructing the loaded previewer to load the attached document and to generate the visual preview of the attached document, wherein the loaded previewer provides one or more interfaces for receiving user input and allowing the visual preview of the attached document to be paged through and navigated.