Developer: Outlook COM Add-in and Large Address Aware

  • Article

Starting from build 16.0.8528.2147 (Version 1709) of the 32-bit version of Outlook 2016 for Windows has been updated to be Large Address Aware (LAA). This increases the maximum address space available to Outlook from 2 GB to 4 GB when it is running on a 64-bit version of Windows. This is key to improved graphics rendering in Outlook when using newer displays that support higher screen resolutions.

  • LAA Outlook has been extensively tested. But there is the possibility that some third-party or in-house developed Outlook COM Add-ins may experience issues with the change.
  • Only 32-bit, 1709 versions of Outlook 2016 or later and running on a 64-bit version of Windows may be impacted.
  • The symptoms may range from COM Add-ins that crash or that exhibit unexpected behaviour or errors.
  • Outlook’s current design automatically disables any COM add-ins that crash.
  • Office store/Office.js add-ins are not be impacted by the LAA
    change.

So what’s for the app developer?

  • So if you are a developer, you should review your COM Add-in code.
  • Test and determine if the add-in is updated for LAA.
  • Ensure it is LAA compatible and not checking for or expecting the high bit to be unset.
  • If the COM Add-in is not updated to work with LAA, the use of the COM Add-in must be reassessed since indefinitely disabling automatic updates to Office is not recommended.

For more info, please refer the detailed info at,

Hope this helps.