How Windows Mobile 6.5 Synced Tasks with Outlook

Windows Mobile 6.5 synchronized task lists with Microsoft Outlook using two primary methods: local synchronization via a PC running specialized bridge software, and direct over-the-air (OTA) synchronization through Microsoft Exchange Server. Whether connected via USB cable or wireless data, the operating system used the Pocket Outlook Object Model (POOM) to map Outlook task fields—such as due dates, priorities, and status—to the mobile device's local database.

Local PC Synchronization (ActiveSync and WMDC)

For standalone desktop Outlook users, synchronization occurred by tethering the Windows Mobile 6.5 device to a personal computer via USB, Bluetooth, or infrared. The synchronization pipeline depended on the host computer's operating system:

  • Windows XP: Relied on Microsoft ActiveSync (version 4.5).
  • Windows Vista and Windows 7: Relied on the Windows Mobile Device Center (WMDC).

Once connected, the desktop software communicated with Outlook using the Messaging Application Programming Interface (MAPI). The user configured a "Partnership" between the phone and the PC, selecting "Tasks" as one of the designated sync categories.

During synchronization, the software compared the desktop Outlook task store (.pst or .ost) with the device’s internal database (initially CEDB, later EDB). The system used unique record identifiers to reconcile differences. If a task was modified on both ends simultaneously, predefined conflict-resolution rules determined whether the PC or the mobile device took precedence.

Over-the-Air (OTA) Synchronization via Exchange ActiveSync

In enterprise environments, Windows Mobile 6.5 bypassed the desktop computer entirely using Exchange ActiveSync (EAS). This protocol connected the device directly to a corporate Microsoft Exchange Server (such as Exchange 2003, 2007, or 2010) over a cellular connection or Wi-Fi.

Exchange ActiveSync utilized XML-based commands over HTTP/HTTPS to synchronize data. When a task was created, updated, or marked complete:

  1. Direct Push: The server maintained a pending HTTP connection with the device. When task updates occurred in the user's Exchange mailbox, the server notified the device immediately.
  2. Payload Sync: The mobile device issued a sync request, and the server delivered only the delta (the changes) in a compressed format to minimize bandwidth.
  3. Local Mapping: Windows Mobile’s messaging layer translated the incoming XML payload into native task properties, updating the built-in Tasks application.

Data Mapping and Limitations

The built-in Tasks application in Windows Mobile 6.5 supported the core metadata of Microsoft Outlook Tasks, including:

  • Subject and body text
  • Start dates, due dates, and reminders
  • Priority levels (Low, Normal, High)
  • Completion status and recurring patterns
  • Categories

However, advanced desktop Outlook features, such as custom task forms, certain complex recurrence rules, or assigned task workflows between team members, were either flattened or stripped to ensure compatibility with the mobile device's more constrained architecture.