Microsoft Exchange Server 2013 : Site mailboxes (part 2) - How site mailboxes work - Synchronization between Exchange and SharePoint

Synchronization between Exchange and SharePoint

Exchange synchronizes with SharePoint by using the SharePoint REST API to fetch the metadata used to display information about documents stored in the site mailbox, including document title, author, last modified date, checked-out status, and the user who last modified the item. Information held in the documents library is synchronized and presented alongside all the other folders in the site mailbox so that the data from the two sources seems as though it originates from a common repository. Items added to a document library through Outlook appear in italics to indicate that the synchronization is not yet complete. In other words, the item has been added to the Exchange mailbox but not yet copied (or published) to SharePoint. After SharePoint has accepted the item and stored it in the document library, the italics are removed and not displayed by Outlook.

If you add more than one document library to the SharePoint quick launch menu, Exchange will synchronize the items from each library into a separate folder. As used in the example discussed here, the default name for a document library on a SharePoint site is Documents, and this is the folder name seen in Outlook. The library could also be called Shared Documents, Project Documents, or whatever other name you assign to it.

In general, the synchronization process between Exchange and SharePoint is reasonably fast, and new items added through one interface appear in the other soon after they are added. If you add a new document library through SharePoint, it will soon appear as a folder in Outlook. Likewise, if you drag an item from Windows Explorer or File Explorer and drop it into the Outlook folder, the item will be synchronized to the SharePoint site within a few minutes. The same is true if you drag and drop items from other Outlook folders into the site folder. You can even create a subfolder for the site folder in Outlook, and it synchronizes with SharePoint. Items placed in the subfolder will also be synchronized with SharePoint. All of this works very well and makes the site mailbox a very approachable repository for anyone who knows how to work with Outlook. The sole downside is that you cannot drag items out of any folder that is synchronized with SharePoint to Windows Explorer (or File Explorer) or another Outlook folder; traffic is unidirectional—into the folder. In addition, if you forward or otherwise reference an item shored in a synchronized folder, the item is not sent as an attachment. Instead, a link to the SharePoint site is embedded in the message to allow the recipient to access the content by clicking the link.

Synchronization is user-driven. In other words, although information about a new site or document library or changes to site membership need to be updated as quickly as possible, information about the contents of a document library might not be so time-critical, especially for document libraries that are not updated very often. To make sure that Exchange and SharePoint remain synchronized, a timer job runs on the Exchange mailbox servers every six hours to make a request to SharePoint for information about new members, documents, and so on. However, if a site is actively used (documents or members are added), Exchange synchronizes with SharePoint every five minutes, and if a site is open in either SharePoint or Outlook, synchronization occurs every fifteen minutes even if items are not added or otherwise updated.

Failure of items to appear in a timely manner in either Exchange or SharePoint is an indication that something is wrong with the synchronization process. If this happens, you can check the last synchronization status by selecting the site mailbox in Outlook. Right-click it and select Site Mailbox Properties from the menu. This leads to a webpage (using EAC) that shows information about the site mailbox, including a Sync Status option. Here you’ll find the date and time of the last successful synchronization together with any error messages plus options to start synchronization. A useful Email Me Details option is provided that requests Exchange to send you a message containing some diagnostic information about the synchronization.

Information about each document is stored as properties of a stub item in the folder used to represent the document library in the site mailbox, including the URL pointing to the item in SharePoint. If you examine the contents of the Documents folder by using MFCMAPI, you can see the properties of the SharePoint items that Exchange synchronizes. When Outlook connects to the site mailbox, it retrieves data about email items from other folders as usual and uses the stub items in the Documents folder to construct the view of the information held in SharePoint.

Using stub items enables Outlook to have faster display access to items in the document library. When Outlook needs to retrieve content for an item held in SharePoint, it passes the URL of the item to the native application for the item. The application checks the Office Document Cache to determine whether an offline copy exists or whether it needs to retrieve a copy from SharePoint. A local copy might exist in the PC’s local cache or because of a previous synchronization with the document library to create an offline copy. When the correct location for the content is determined, the application retrieves and opens the item. As far as the application is concerned, it has received a request to open and process content and does not care about its source. Although it is usual to store mail messages in Exchange rather than in a document library, you can move messages to a document library for purposes such as marking the messages as immutable records. Messages are stored in document libraries as .msg files, and Outlook opens these items. Logically, if you open an item such as a Word document or a PowerPoint presentation that is checked out to another user, you will not be able to update the content.

Figure 1 shows how items in a site mailbox are accessed through Outlook 2013. In this case, a site mailbox called Project Alpha is open. The Inbox, Deleted Items, and Junk Email folders are stored in a mailbox database that Exchange manages. The view of items in the Documents folder is constructed from the stub items. The properties synchronized to the stub items from SharePoint are sufficient to present an informative view to the end user.

Figure 1. How Outlook 2013 displays a site mailbox and its contents

If you run the Get-MailboxFolderStatistics cmdlet to report on information held in a site mailbox, it reports the number of items and the size of the items held in the Documents folder. The number of items is correct, but the item size represents only the much smaller stub items that hold the properties describing the real documents that are synchronized from SharePoint.

Because Outlook provides the interface for site mailboxes, some of the advanced document management features available within SharePoint are not exposed. For example, you can’t see prior versions of documents that are stored on the SharePoint site with Outlook, and you can’t check out a document to reserve it against editing by other users. These features are available by connecting to the underlying SharePoint site with a browser. The easiest way to access the underlying site for a document library is to select the library in Outlook, right-click it, and select Open In Web Browser from the menu. Figure 2 illustrates the situation after you have connected to the same Project Alpha site as accessed through SharePoint through a browser. The same items Outlook presents in the Documents folder are visible, but now some additional options such as document checkout are available because the web interface supports the options.

Figure 2. The same site viewed through Microsoft Internet Explorer