After Installing 2024-04 Windows Update, Both New and Old Outlook Unusable

Question

After Installing 2024-04 Windows Update, Both New and Old Outlook Unusable

Alex Rourke 306

After installing the April 2024 Windows Update, about a third of our devices (running Windows 11 25H2) are having major issues with Outlook. Classic Outlook freezes when a new email is received and must be killed from task manager. New Outlook freezes immediately when it is launched in some cases and in other cases, won't launch at all:

This happens on brand new newly provisioned computers.
Office, New Outlook, and all Edge components are up-to-date.
Repairing/reinstalling Outlook/Office or recreating profiles does not resolve the issue.
Disabling all add-ins in Outlook does not resolve the issue, nor does running it in safe mode.
SFC /scannow finds corruption on every computer we run it on following the latest update.

This is only impacting some users, particularly users that monitor shared mailboxes. With both Outlooks broken, their ability to work is severely compromised.

UPDATE 6/12/26: I've created a new and more detailed post in hopes that the right person would see this, that post is linked here: Windows 11 April 2026 Cumulative Update causes app crashes every ~24 hours (Outlook + Explorer) - resolved by user logoff

Aaron M 5 Reputation points

2026-04-23T15:57:54.3833333+00:00

Hey @Alex Rourke , We also have the same problem on a few machines. Currently we have been made aware of 4 different computers. I wanted to update this thread, because it's the typical reply from Microsoft denying responsibility. Same sort of issues you have described, but I don't think it's freezing, it's merely not retrieving email after sometime. They have to close outlook classic and reopen to have it pull in M365 emails again. It's the same criteria as you DISM corruption, etc.
Alex Rourke 306 Reputation points

2026-04-23T16:08:10.5066667+00:00

@Aaron M, I couldn't get my post to tag you, so I hope you see this! Interestingly, we set up a new computer for one of the impacted users, verified that Outlook worked without the April update, then updated the computer to the April update. Surprisingly, the computer worked just fine. The one notable difference between this computer and the others is that the new computer was running Office Build 2604 whereas the computers having the issue were running build 2603.

I posted about this on Reddit and a commenter there said this issue is occurring for them in 2604 as well, which makes narrowing down the issue difficult.

Without being able to recreate the issue consistently, I'm worried I'll be wasting my time opening a ticket with Microsoft, as they usually (desperately) try to drive you to paid support or to close the ticket, but we have to take the April update at some point.

Based on the number of users facing this, if in fact a freshly built machine fixed the issue, we're tempted just to reset and re set up the user's machines. This is a PITA, but it couldn't be any more of a pain than dealing with Microsoft support.
Aaron M 5 Reputation points

2026-04-23T17:24:48.6+00:00

@Alex Rourke That was probably me. I noticed it on 2 different versions as well. and that basically threw that theory out the window for me. I'm a 1-man MSP so trying to find others with similiar issues is very hard. Then I found your post. It just seems like when the email stops coming in after awhile, closing and reopening it again brings what was not showing in the inbox(es). rinse and repeat. not really efficient for people trying to get work done. I'm going to attempt to remove the 2026-04 Security update on one of the affected computers, that was applied on the weekend when this stuff started being noticeable on Monday/Tuesday from one client. Now I have 2 clients with the same issue. Mobile Outlook and web are fine.

i was going to do a resolve issues with windows update, but some of these machines won't give the option to do that since winRE is buggered up since. Hopefully I can remove the update via settings.
Aaron M 5 Reputation points

2026-04-26T13:23:20.2033333+00:00

Hey @Alex Rourke Have you attempted to reinstall the 2025-04 Security update after removing it? If so what was the outcome to that?
Alex Rourke 306 Reputation points

2026-06-08T15:32:04.39+00:00

@Aaron M Unfortunately uninstalling and reinstalling the update does not resolve anything, and this has not been resolved by the updates that have rolled out since then (either to Windows or to Office). We have imaged brand new computers with the April update to test this and - for the impacted users - they always end up failing. For a few users, things have gotten even worse - both new and classic Outlook crash when a new email is received and usually freeze or crash Windows Explorer with them. The only thing that resolves the issue permanently is uninstalling the 2026-04 security update.

There are some workarounds that seem to work OK, though they are not ideal. Rebooting the computer once the freeze occurs once resolves the issue for almost exactly 24 hours (almost to the minute). Asking a user to reboot their computer every day when this happens is not great, but it is effective. Another option that seems to work is enabling troubleshooting mode in Outlook, though this slows Outlook down and produces a lot of log files.

Microsoft Support has been useless helping us with this. They don't respond to emails for days at a time, they ignore the content of email that doesn't suit them, they repeatedly send irrelevant AI generated troubleshooting steps that are not at all relevant to the issue at hand. All the while they keep telling me they know it is important and they are working on it. They ask my availability for a call and then don't respond to my emails until I follow up with them several times. Rinse and repeat over and over.
Alex Rourke 306 Reputation points

2026-06-12T15:24:12.79+00:00

We had a meeting with Microsoft about this today. I sent an email setting expectations before the meeting began. I waited in the meeting for 20 minutes and the support agent never showed up. Microsoft support is horrendous. It is clear they are not taking this issue seriously and lack the capacity to take properly serve their customers.
Alex Rourke 306 Reputation points

2026-06-16T15:13:01.82+00:00

Further testing has revealed that this issue is very likely with the Windows Notification Service and that Outlook is just triggering the crash as an app that produces a lot of notifications. We're also seeing evidence in our environment that this issue may have been resolved by KB5094126. It will take some time to confirm whether or not this is true (because Microsoft never acknowledged this was an issue, nor do they indicate that it was resolved by this update), but it is looking promising.

1 answer

Your answer

Aaron M 5 Reputation points

2026-04-23T15:57:54.3833333+00:00

Hey @Alex Rourke , We also have the same problem on a few machines. Currently we have been made aware of 4 different computers. I wanted to update this thread, because it's the typical reply from Microsoft denying responsibility. Same sort of issues you have described, but I don't think it's freezing, it's merely not retrieving email after sometime. They have to close outlook classic and reopen to have it pull in M365 emails again. It's the same criteria as you DISM corruption, etc.
Alex Rourke 306 Reputation points

2026-04-23T16:08:10.5066667+00:00

@Aaron M, I couldn't get my post to tag you, so I hope you see this! Interestingly, we set up a new computer for one of the impacted users, verified that Outlook worked without the April update, then updated the computer to the April update. Surprisingly, the computer worked just fine. The one notable difference between this computer and the others is that the new computer was running Office Build 2604 whereas the computers having the issue were running build 2603.

I posted about this on Reddit and a commenter there said this issue is occurring for them in 2604 as well, which makes narrowing down the issue difficult.

Without being able to recreate the issue consistently, I'm worried I'll be wasting my time opening a ticket with Microsoft, as they usually (desperately) try to drive you to paid support or to close the ticket, but we have to take the April update at some point.

Based on the number of users facing this, if in fact a freshly built machine fixed the issue, we're tempted just to reset and re set up the user's machines. This is a PITA, but it couldn't be any more of a pain than dealing with Microsoft support.
Aaron M 5 Reputation points

2026-04-23T17:24:48.6+00:00

@Alex Rourke That was probably me. I noticed it on 2 different versions as well. and that basically threw that theory out the window for me. I'm a 1-man MSP so trying to find others with similiar issues is very hard. Then I found your post. It just seems like when the email stops coming in after awhile, closing and reopening it again brings what was not showing in the inbox(es). rinse and repeat. not really efficient for people trying to get work done. I'm going to attempt to remove the 2026-04 Security update on one of the affected computers, that was applied on the weekend when this stuff started being noticeable on Monday/Tuesday from one client. Now I have 2 clients with the same issue. Mobile Outlook and web are fine.

i was going to do a resolve issues with windows update, but some of these machines won't give the option to do that since winRE is buggered up since. Hopefully I can remove the update via settings.
Aaron M 5 Reputation points

2026-04-26T13:23:20.2033333+00:00

Hey @Alex Rourke Have you attempted to reinstall the 2025-04 Security update after removing it? If so what was the outcome to that?
Alex Rourke 306 Reputation points

2026-06-08T15:32:04.39+00:00

@Aaron M Unfortunately uninstalling and reinstalling the update does not resolve anything, and this has not been resolved by the updates that have rolled out since then (either to Windows or to Office). We have imaged brand new computers with the April update to test this and - for the impacted users - they always end up failing. For a few users, things have gotten even worse - both new and classic Outlook crash when a new email is received and usually freeze or crash Windows Explorer with them. The only thing that resolves the issue permanently is uninstalling the 2026-04 security update.

There are some workarounds that seem to work OK, though they are not ideal. Rebooting the computer once the freeze occurs once resolves the issue for almost exactly 24 hours (almost to the minute). Asking a user to reboot their computer every day when this happens is not great, but it is effective. Another option that seems to work is enabling troubleshooting mode in Outlook, though this slows Outlook down and produces a lot of log files.

Microsoft Support has been useless helping us with this. They don't respond to emails for days at a time, they ignore the content of email that doesn't suit them, they repeatedly send irrelevant AI generated troubleshooting steps that are not at all relevant to the issue at hand. All the while they keep telling me they know it is important and they are working on it. They ask my availability for a call and then don't respond to my emails until I follow up with them several times. Rinse and repeat over and over.
Alex Rourke 306 Reputation points

2026-06-12T15:24:12.79+00:00

We had a meeting with Microsoft about this today. I sent an email setting expectations before the meeting began. I waited in the meeting for 20 minutes and the support agent never showed up. Microsoft support is horrendous. It is clear they are not taking this issue seriously and lack the capacity to take properly serve their customers.
Alex Rourke 306 Reputation points

2026-06-16T15:13:01.82+00:00

Further testing has revealed that this issue is very likely with the Windows Notification Service and that Outlook is just triggering the crash as an app that produces a lot of notifications. We're also seeing evidence in our environment that this issue may have been resolved by KB5094126. It will take some time to confirm whether or not this is true (because Microsoft never acknowledged this was an issue, nor do they indicate that it was resolved by this update), but it is looking promising.

Answer 1

Anonymous

Hi @Alex Rourke,

Good day, I hope you are doing well.

Thank you for your patience, and I appreciate the time you have already spent troubleshooting this issue. I understand how disruptive this is, especially since it is still affecting multiple users and both classic Outlook and new Outlook remain impacted.

Since the issue is still occurring after the standard troubleshooting steps and is affecting multiple users, it appears to require a deeper investigation at the backend level. While I would love to resolve this directly, my current scope and resource limitations do not allow access to the internal systems needed for this type of troubleshooting. The best next step is to have your IT administrator submit a support ticket through the Microsoft 365 Admin Center.

Once the ticket is created, a technical support engineer will be able to initiate a secure remote session, review backend configurations, run diagnostics, and escalate the case to specialized engineering teams if necessary. These teams are equipped to perform advanced troubleshooting and provide targeted solutions.

As moderators, our role is to offer guidance and general troubleshooting steps. Although we do not have access to administrative tools required for backend fixes, we truly appreciate your understanding of these limitations. We hope the information provided helps point you in the right direction, and we are always here to assist as much as possible within our scope.

For instructions on submitting a support request, please refer to: Get support - Microsoft 365 admin | Microsoft Learn.

I hope you found the answer helpful, and I would greatly appreciate it if you could mark it as accepted. This helps highlight the solution for others who may be searching for similar information in the community. Your contribution not only supports fellow users in finding the right guidance more quickly, but also helps build a more resourceful and collaborative space for everyone.

Thank you for your kindness and contributions to the forum.

If you have extra questions about this answer, please click "Comment".

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Alex Rourke 306 Reputation points

2026-04-21T14:51:55.83+00:00

We are doing a little more testing before bringing this to Microsoft (I am the admin), but to anyone else who finds this thread. It is worth noting that uninstalling the April 2026 Windows update immediately resolved the issue for every user experiencing it.
Anonymous

2026-04-21T17:29:15.44+00:00

Hi @Alex Rourke,

Thank you for your update. I appreciate your time reviewing the information, and I'm glad that you were able to resolve the issue for your users by uninstalling the Windows update.
If you have any further questions or need additional assistance, please feel free to reach out and let me know. I'll be happy to help.

Wishing you a great day ahead.
Alex Rourke 306 Reputation points

2026-06-08T15:34:21.8766667+00:00

I'm commenting here to leave this open, as I explain in another comment, Microsoft Support has been worthless, and this continues to be an issue. Our hope was that their lack of responsiveness was because they knew this was a problem and were going to fix it, but two months on, I no longer think that is true.

Outlook is arguably the most important app in their stable of apps, and it is broken. We are beginning the painful process of evaluating alternatives to all Microsoft solutions we currently use because we see no resolution to this issue in sight.
Anonymous

2026-06-09T22:44:36.87+00:00

Hi @Alex Rourke,

I appreciate your time sharing your concern after contacting Microsoft Support, and I'm sorry to hear that the support agent did not respond to your email for several days.

To better assist, I have initiated a private message to ask for more details regarding your ticket. When you have a moment, please click View message at the top of the thread. This will allow secure and direct access to information.

Thank you for your time and patience. I'm looking forward to your response.
James E. Mahone 0 Reputation points

2026-11-02T18:01:32.6566667+00:00

When I attempted to open MS Outlook 2016 this afternoon (2 p.m., Nov. 2, 2026), the program would not open after repeated tries. Used the repair function that was suggested online, but Outlook still would not open.
Hornblower409 18,420 Reputation points

2026-11-03T01:38:12.91+00:00

@James E. Mahone said

When I attempted to open MS Outlook 2016 this afternoon (2 p.m., Nov. 2, 2026), the program would not open

I understand that you have the same or similar issue to the one discussed in this thread. But you will probably not get any help by adding to an old post.

I would suggest that you start a new thread using the "Ask a question" button at the top of this page to create a new Question and include the details for your specific problem and what steps you have already tried to fix it.

This provides much higher visibility to your issue than adding on to an existing post, which is only seen by people who are already following this question.