Are there any commonalities between the affected users beyond just the version of Outlook you are using?

Slow, stuttering, freezing, email delays etc. in Outlook I have seen previously be associated with excessive OST file sizes.

How large are the mailboxes in question?
How many folders are the users creating in them?
What about shared mailboxes? Do these users collaborate with shared mailboxes?

Shared mailboxes in cached exchange still store to the same OST file as the main users mailbox. So even if their personal mailbox is within a normal file size range, the shared mailboxes could be tipping Outlook over the edge.

It doesn’t help that it appears that Outlook runs its GUI tasks and database tasks in the same threads. So when it gets busy it freezes up, as opposed to not freezing and showing a “busy” status somewhere for the user to see.

If shared mailboxes are involved… Get the user to use OWA for a time to access the mailbox, and remove it from the desktop Outlook. See how they go.
Whilst they are doing that take a closer look at the folder counts and mailbox sizes.

The folder limit for shared mailboxes was recently increased, but in my experience if you’re at that kind of number of folders, even if officially supported, you’ll still see issues. So double check that and if you notice a stupid number of folders try to consult the users into reducing the number.

If you determine it to be a OST file size issue… I have previously setup affected users with their shared mailbox by adding it as a secondary account in Outlook and then remove the automapping portion of their permission to that mailbox. They will add the account with the mailboxes actual email address, but when asked to authenticate they will use their own personal credentials not the mailboxes. The reason I did this is that adding the shared mailbox as a separate account makes it use its own OST file.

Answer from chris43263458 on community.spiceworks.com
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Microsoft
microsoft.com › en-us › download › details.aspx
Download Update for Microsoft Outlook 2016 (KB4493226) 32-Bit Edition from Official Microsoft Download Center
Microsoft has released an update for Microsoft Outlook 2016 32-Bit Edition. This update provides the latest fixes to Microsoft Outlook 2016 32-Bit Edition. Additionally, this update contains stability and performance improvements.
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ManageEngine
manageengine.com › products › desktop-central › patch-management › Outlook-2016-updates.html
Outlook 2016 Updates | ManageEngine Desktop Central
Outlook 2016 Patches · Back to list · Disclaimer: This webpage is intended to provide you information about patch announcement for certain specific software products. The information is provided "As Is" without warranty of any kind. The links provided point to pages on the vendors websites.
Discussions

Outlook Requires Updates | Office Software
Hi all, Have a user who has Office 2016 Pro Plus installed on their laptop. They cannot use Outlook as the message is asking to update from version 16.0.4266.1001 to 16.0.4600.1000. I have tried the 'install updates' option and also checked out any updates it says are required but the message sti... More on edugeek.net
🌐 edugeek.net
May 13, 2022
Is Outlook 2016 Standard 32bit a bad idea in a Windows 10 Pro 64bit environment
Lately we have been having a really hard time with Outlook help desk tickets. All of the tickets have the same issues such as Outlook not responding, crashing, or failing to recieve emails in a timely manner. This happens when in the office, and out of the office,on VPN and off the VPN. More on community.spiceworks.com
🌐 community.spiceworks.com
9
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February 11, 2021
I'm losing my mind.... Office 2016 32bit self upgraded to Office 2016 (365) 64bit
Are you sure it isn't "Microsoft Desktop Apps", or some other click to run variant? I typically find unless I forcefully remove both clicktorun, and "MS Desktop Apps" they come back just like candy-crush, and the other Windows Store Apps. More on reddit.com
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How to Update Office 2016 from 16.0.4266 to 16.0.4600?
Hey all. I appreciate you checking this questions out as I’m open to any constructive suggestions. We have Office Professional Plus 2016 x86 running on Windows 10 Ent. Due to a change in security procedures, we’ve been directed to update our Office (specifically Outlook) to version 16.0.4600. More on community.spiceworks.com
🌐 community.spiceworks.com
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January 6, 2023
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Microsoft
microsoft.com › en-us › download › details.aspx
Download Update for Microsoft Outlook 2016 (KB3127988) 32-Bit Edition from Official Microsoft Download Center
July 15, 2024 - Microsoft has released an update for Microsoft Outlook 2016 32-Bit Edition. This update provides the latest fixes to Microsoft Outlook 2016 32-Bit Edition. Additionally, this update contains stability and performance improvements.
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Microsoft Support
support.microsoft.com › en-us › topic › july-1-2025-update-for-outlook-2016-kb5002747-b18b9510-c6e7-4325-b760-73b635db42af
July 1, 2025, update for Outlook 2016 (KB5002747) - Microsoft Support
July 1, 2025 - Download update for Microsoft Outlook 2016 (KB5002747)​​​​​​​ · If you're not sure which platform (32-bit or 64-bit) you're running, see Am I running 32-bit or 64-bit Office?
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EduGeek
edugeek.net › forums › technical › office software
Outlook Requires Updates | Office Software
May 13, 2022 - Hi all, Have a user who has Office 2016 Pro Plus installed on their laptop. They cannot use Outlook as the message is asking to update from version 16.0.4266.1001 to 16.0.4600.1000. I have tried the 'install updates' option and also checked out any updates it says are required but the message sti...
🌐
Microsoft
microsoft.com › en-us › download › details.aspx
Download Security Update for Microsoft Outlook 2016 (KB4504712) 32-Bit Edition from Official Microsoft Download Center
July 15, 2024 - A security vulnerability exists in Microsoft Outlook 2016 32-Bit Edition that could allow arbitrary code to run when a maliciously modified file is opened. This update resolves that vulnerability.
Top answer
1 of 9
1

Are there any commonalities between the affected users beyond just the version of Outlook you are using?

Slow, stuttering, freezing, email delays etc. in Outlook I have seen previously be associated with excessive OST file sizes.

How large are the mailboxes in question?
How many folders are the users creating in them?
What about shared mailboxes? Do these users collaborate with shared mailboxes?

Shared mailboxes in cached exchange still store to the same OST file as the main users mailbox. So even if their personal mailbox is within a normal file size range, the shared mailboxes could be tipping Outlook over the edge.

It doesn’t help that it appears that Outlook runs its GUI tasks and database tasks in the same threads. So when it gets busy it freezes up, as opposed to not freezing and showing a “busy” status somewhere for the user to see.

If shared mailboxes are involved… Get the user to use OWA for a time to access the mailbox, and remove it from the desktop Outlook. See how they go.
Whilst they are doing that take a closer look at the folder counts and mailbox sizes.

The folder limit for shared mailboxes was recently increased, but in my experience if you’re at that kind of number of folders, even if officially supported, you’ll still see issues. So double check that and if you notice a stupid number of folders try to consult the users into reducing the number.

If you determine it to be a OST file size issue… I have previously setup affected users with their shared mailbox by adding it as a secondary account in Outlook and then remove the automapping portion of their permission to that mailbox. They will add the account with the mailboxes actual email address, but when asked to authenticate they will use their own personal credentials not the mailboxes. The reason I did this is that adding the shared mailbox as a separate account makes it use its own OST file.

2 of 9
4

Lately we have been having a really hard time with Outlook help desk tickets. All of the tickets have the same issues such as Outlook not responding, crashing, or failing to recieve emails in a timely manner. This happens when in the office, and out of the office,on VPN and off the VPN. I’ve always felt like we were behind the times by staying on Office 2016 and using the 32bit version. Am I wasting time by trying to get my organization to upgrade? We have migrated to Exchange Online but we don’t have the ability to download and install from Office online. We are still manually installing our old 2016 copy of Office. Would using the old version of Office cause problems like we’ve been seeing? I’m really at my wit’s end with all of these Outlook issues. I’ve removed all add-ins and done Office repairs and used the Microsoft SaRA to try and find a problem but nothing is working.

Find elsewhere
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Microsoft Learn
learn.microsoft.com › en-us › officeupdates › outlook-updates-msi
Latest updates for versions of Outlook that use Windows Installer (MSI) - Office release notes | Microsoft Learn
October 24, 2025 - Use the links on this page to get more information about and download the most recent updates for the perpetual version of Outlook 2016.
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Microsoft Support
support.microsoft.com › en-us › topic › april-10-2025-update-for-office-2016-kb5002623-d60c1f31-bb7c-4426-b8f4-69186d7fc1e5
April 10, 2025, update for Office 2016 (KB5002623) - Microsoft Support
April 10, 2025 - This update fixes the known issue in KB 5002700 that causes Microsoft Word, Microsoft Excel, and Microsoft Outlook to stop responding. Note: To restore the full Office 2016 suite to a working state, you must have both updates KB 5002700 and KB 5002623 installed.
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Reddit
reddit.com › r/sysadmin › i'm losing my mind.... office 2016 32bit self upgraded to office 2016 (365) 64bit
r/sysadmin on Reddit: I'm losing my mind.... Office 2016 32bit self upgraded to Office 2016 (365) 64bit
January 4, 2019 -

Ok.... I've checked everything I can think of. I've checked SCCM. I've checked event logs where you can see it happening. I've checked updates NOTHING!

I have a user and a laptop which overnight (4pm) decided to upgrade it's 2016 32bit version of office to 2016 (365 pro plus) 64bit which is fantastic as I want to do that globally for all users..... But how in the ever loving shit did it manage to do it?!

I was on the laptop myself earlier in the day. Only thing I did was add Skype for business addin to active in the registry. I can see the upgrade happening in the event logs going from office15 to office16 and registering all the keys to each application. I am utterly bamboozled.

There is no indication whatsoever to trigger this.

OS: Windows 10 1903.

Office: 2016 32bit to 2016 64bit pro plus.

Licence: E3.

Only software even remotely 365 installed: Teams.

I'm half tempted to open a MS ticket as I really hope this is something that's a real thing and I can push out globally. Please tell me it's really simple and I'm an idiot. I can take it hah!

🌐
Google
tools.google.com › dlpage › gssmo
Download Google Workspace Sync for Microsoft® Outlook® - Google
DOWNLOAD .EXE FILE (RECOMMENDED FOR USERS) This .exe file is for installation on Windows® machines only but you can download it using any operating system. Download GWSMO DOWNLOAD .MSI FILE (RECOMMENDED FOR ADMINS) This .msi file is for installation on Windows machines only but you can download it using any operating system. Download 32-bit edition | Download 64-bit edition
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Softonic
microsoft-outlook.en.softonic.com › home › windows › productivity › e-mail clients › microsoft outlook
Microsoft Outlook - Download
December 4, 2024 - Microsoft Outlook, free and safe download. Microsoft Outlook latest version: Download Microsoft Outlook for Windows: Sending emails and scheduling jus
Rating: 6.5/10 ​ - ​ 3.16K votes
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Robert 365
robert365.com › home › upgrading to outlook 2016
Upgrading to Outlook 2016 - Robert 365
July 24, 2025 - If you still aren’t being updated ... has been prepared, you can run the installer to install Office 2016. By default, it will install the 32-bit edition unless you specifically tell it not to....
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Slipstick.com
forums.slipstick.com › microsoft outlook › using outlook
Outlook 2016 Will Not Show Any Data In the People Pane | Outlook Forums by Slipstick.com
November 19, 2017 - Nothing shows up under the people ... thought maybe the issue was related to an update, so I completely reformatted my hard drive and re-installed office and still the problem persists. I am running Office 365 with Outlook 2016 32 bit (not exchange server) and my system is a Dell ...
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Super User
superuser.com › questions › 1164479 › office-outlook-2016-32-bit-text-box-and-button-heights-not-displaying-correctl
Office Outlook 2016 (32-bit) text box and button heights not displaying correctly - Windows 10 (64-bit) - Super User
January 7, 2017 - The text box and button height in the new email window in Office Outlook 2016 does not display correctly. Please see image attached. Shouldn't the text boxes on the right have the same height as the buttons (From, To, Cc) on the left? ... I am using Windows 10 64-bit and Office 2016 32-bit.
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Microsoft Support
support.microsoft.com › en-us › topic › november-7-2023-update-for-outlook-2016-kb5002523-ab90c2b6-4a36-4467-9d0e-2b30c14f8f5f
November 7, 2023, update for Outlook 2016 (KB5002523) - Microsoft Support
November 7, 2023 - This update fixes an issue in which ... This update is also available for manual download and installation from the Microsoft Download Center. Download update 5002523 for the 32-bit version of Outlook 2016...