Developer: Outlook COM Add-in and Large Address Aware


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.

Comments (2)
  1. Extremely powerful article. Thanks for sharing man

    1. Deva [MSFT] says:

      Thanks Uniben!!

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