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.
How does this affect me?
While LAA Outlook has been extensively tested, there is the possibility that some third-party or in-house developed Outlook COM Add-ins may experience issues with the change. Again, 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 behavior or errors. Outlook’s current design automatically disables any COM add-ins that crash. Note that Office store add-ins are not be impacted by the LAA change.
What are the steps I should take if I see issues with COM add-ins?
As an end user
If you experience crashes or unexpected behavior with COM add-ins, please contact your IT department and ask them to test and determine if the add-in is updated for LAA.
As an IT administrator
A COM Add-in developer may have built the solution under the assumption that Outlook would never support more than 2 GB of address space and thus used the higher address space to store other state data. With the new design allowing the higher address space to now be allocated, the COM Add-in may improperly write to that address space or find unexpected data in that space.
If the COM Add-in is developed by a third-party vendor, please contact that vendor to report the issue and to ask if their COM Add-in has been or is being updated. For any COM Add-ins developed in-house, report the issue to your internal developer.
If the COM add-in is business critical to your organization, you may revert the Office 2016 Click-to-Run installation to an earlier build. Note that the LAA functionality is built into Outlook 2016. Therefore, it is not a separate feature that can be disabled by Group Policy, a registry value or via the user interface.
To revert to an earlier version of Office 2016, you must disable automatic updates in Office, install a previous build, and then after the add-in has been updated to work with LAA, re-enable automatic updates in Office. For more information on reverting to an earlier version of Office 2016, please see How to revert to an earlier version of Office 2013 or Office 2016 Click-to-Run.
It is important to note that 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.
To identify COM Add-ins that cause Outlook to crash, see Add-ins are user re-enabled after being disabled by Office programs.
If you are a developer, you should review your COM Add-in code to ensure it is LAA compatible and not checking for or expecting the high bit to be unset.