Edit: we've published an additional help article about this update: https://support.office.com/en-us/article/Large-Address-Aware-in-Outlook-2016-ea0913e4-2917-4456-b0ea...


We'd like to tell you about an an upcoming change in the Office 365 subscription version of Outlook 2016 for Windows that may affect you. Starting in version 1709, the 32-bit version of Outlook will be Large Address Aware (LAA).  What does this mean and how will it impact you?  Read on for more details.


In Windows, normal 32-bit executables have a maximum address space of 2GB. This has been the case for many years.  In those years, however, hardware has moved on and has massively increased its capability.  In particular, machines today have much more memory as well as increasingly higher resolution displays.  In particular, the resolution of displays is the motivating factor for enabling LAA for Outlook.  As displays get larger, the amount of graphics memory required to compose, render, and display applications increases dramatically.  The 2GB limit described above puts pressure on Outlook’s ability to draw all the pixels to the screen—enough pressure that some re-draw glitches might result in some situations.  LAA enabling allows Outlook to have a full 4GB of address space and reduce the chances of those re-draw glitches happening.  Keep in mind that the application won’t necessarily use all of that memory at once, the gains are in having larger contiguous blocks of address space to use in our graphics subsystem.


The casual reader may ask “why should this matter to me?” or “sounds like a good idea, why didn’t you always do this?”  The answer has to do with the history of the 2GB limit for 32-bit processes.  Because 2GB was the highest address that an application would have to utilize, software developers could know that the addresses would only use 31 bits (2GB=2^31).  They could then use the extra “high bit” for any interesting purpose (bookkeeping, for example).  As a result, poorly (or “creatively”) written code may now malfunction in a LAA enabled process.  While LAA Outlook has been extensively tested, there is the possibility that some COM add-ins in Outlook may not be compatible.  Should you experience crashes in Outlook caused by an add-in, the add-in should be disabled, and a warning given when you restart the app.  Please contact the add-in author and request an updated build that is LAA compatible.


All of the above only applies to 32-bit Outlook.  Any customers running 64-bit Outlook are already reaping the benefits of a much MUCH larger address space.


Thanks, and let us know if you have any questions. 

-The Outlook team

Trusted Contributor

Thanks for the heads-up and explanation.  While this sounds like a welcome improvement, it's useful to know that certain COM add-ins may not be compatible with this change and that's something customers should be on the lookout for if they experience issues in Outlook going forward.

Frequent Visitor

Is the solution also going to be availble for MSI installs?


@Sulabh Upadhyaya - no, it will only be available for C2R installs. 

Not applicable

Will we get the warning pop-up when I restart application after crash or I have to go /Manage 'Slow and Disabled COM Add-ins' section to see the COM add-in that is causing the issue?

Established Member


A step in the right direction, but please get this out for MSI users of Office 2016.  We are experiencing the issue during trials of new hardware with higher screen resolutions and see the black bars randomly appear in Outlook.

Occasional Visitor

Thank you very much for the comprehensive article!

Is it a good idea to enable the laa flag (with editbin.exe) for MSI Installations manually ?  and can i enable the flag for Outlook 2010 as well ?

New Contributor

coach-city-zip-orange-leather-tote-23312234-0-1.jpgWhen you follow a group in Outlook, all group conversations and calendar events will be sent to both the group mailbox and your personal inbox. This is particularly helpful when you belong to multiple groups and want to stay on top of the conversations from one location.

Message originators won't receive copies of their messages in their inboxes. 


Follow a group

  1. In Outlook 2016 or Outlook on the web, select a group from the left navigation pane.

  2.  Office 365 group

    Create a space for a team to collaborate, communicate, and schedule events.

     Distribution list

    Create a list that people can use to send the same email message to more than one address.

     Help me choose

    Need tips on picking the right type of group or shared mailbox for your needs?

    At the top of the conversations list, select Not following > Follow in Inbox.