Major issue attaching files after Office update (Version 2606)

Question

Major issue attaching files after Office update (Version 2606)

Pejman Minooei 20

Since applying the June 2026 updates, we are experiencing a critical issue with file attachments in Microsoft 365 Apps.

Affected versions:

Version 2606 (Build 20131.20112) – June 30
Version 2606 (Build 20131.20090) – June 25

Issue: Users are unable to attach files in Outlook and other Office applications.

Workaround: Rolling back to Version 2605 (Build 20026.20182) fully resolves the issue. We have also stabilized the environment by disabling automatic updates and enforcing the previous version via XML configuration.

Impact: Organization-wide disruption affecting client communications (High severity).

Request: Please investigate the root cause of the attachment issue in Version 2606, confirm whether this is a known issue, and provide a timeline for a fix along with a recommended long-term solution.

Best Regards.

Hornblower409 12,265 Reputation points

2026-07-02T05:14:11.4533333+00:00

@Pejman Minooei said

Users are unable to attach files in Outlook and other Office applications.

Just as a data point. I am running Outlook Version 2606 Build 20131.20112 64-bit connected to a MS 365 Business Standard account and not having any problems with Outlook attachments.

When they click on Insert -> Attach file they don't see any suggestion and/or can't browse to a local file or network file?

They can do use the insert menu in Outlook but the file is not attached?

They can attach the file but the email won't send?
Ric Rockwell 10 Reputation points

2026-07-02T14:36:35.91+00:00

We have seen a few issues with this since applying June updates. This has impacted users running both Classic and New Outlook.
Hornblower409 12,265 Reputation points

2026-07-02T14:52:08.0133333+00:00

@Ric Rockwell said

We have seen a few issues with this since applying June updates.

1 -- Same questions as I ask in my previous comment to Pejman. Where exactly in the Attachment process is the problem? Any error messages?

This has impacted users running both Classic and New Outlook.

That's interesting. It would seem to point to something other than just Outlook?

2 -- Are you also having the problem in other Office Apps like Pejman described in the original Question?
Pejman Minooei 20 Reputation points

2026-07-02T20:51:38.8+00:00

@Hornblower409

I used the Office Deployment Tool to deploy Outlook using the XML configuration with Channel="MonthlyEnterprise" and Version="16.0.20026.20166". This stable version has worked for us without any issues.
BrentH 5 Reputation points

2026-07-10T21:34:51.4166667+00:00

As another datapoint, we're having Outlook crashes in our environment starting with 2606 whenever somebody tries to email a PDF from Adobe Acrobat using the "Share" button and then selecting the "Email" option. We also get the same "The operation failed" dialog as is mentioned below.
BrentH 5 Reputation points

2026-07-20T14:57:52.7266667+00:00

Share -> Email from Adobe Acrobat seems to be working again with the 2606 (Build 20131.20154) July 14th release.
T Ferguson 0 Reputation points

2026-07-30T23:58:22.0066667+00:00

I am having a similar problem.

I would say 8 times out of 10 I can not add simple attachments (eg low file size PDFs) to an email, either by dragging and dropping or by using the attach file option from the ribbon at the top.

When I go to attach the file it shows there at the top of the email with the loading bar, but when the loading bar is complete the attachment disappears.

I am on a Mac running macOS Tahoe Version 26.5.2 and Microsoft Outlook for Mac Version 16.98 (25060824)

4 answers

Your answer

Hornblower409 12,265 Reputation points

2026-07-02T05:14:11.4533333+00:00

@Pejman Minooei said

Users are unable to attach files in Outlook and other Office applications.

Just as a data point. I am running Outlook Version 2606 Build 20131.20112 64-bit connected to a MS 365 Business Standard account and not having any problems with Outlook attachments.

When they click on Insert -> Attach file they don't see any suggestion and/or can't browse to a local file or network file?

They can do use the insert menu in Outlook but the file is not attached?

They can attach the file but the email won't send?
Ric Rockwell 10 Reputation points

2026-07-02T14:36:35.91+00:00

We have seen a few issues with this since applying June updates. This has impacted users running both Classic and New Outlook.
Hornblower409 12,265 Reputation points

2026-07-02T14:52:08.0133333+00:00

@Ric Rockwell said

We have seen a few issues with this since applying June updates.

1 -- Same questions as I ask in my previous comment to Pejman. Where exactly in the Attachment process is the problem? Any error messages?

This has impacted users running both Classic and New Outlook.

That's interesting. It would seem to point to something other than just Outlook?

2 -- Are you also having the problem in other Office Apps like Pejman described in the original Question?
Pejman Minooei 20 Reputation points

2026-07-02T20:51:38.8+00:00

@Hornblower409

I used the Office Deployment Tool to deploy Outlook using the XML configuration with Channel="MonthlyEnterprise" and Version="16.0.20026.20166". This stable version has worked for us without any issues.
BrentH 5 Reputation points

2026-07-10T21:34:51.4166667+00:00

As another datapoint, we're having Outlook crashes in our environment starting with 2606 whenever somebody tries to email a PDF from Adobe Acrobat using the "Share" button and then selecting the "Email" option. We also get the same "The operation failed" dialog as is mentioned below.
BrentH 5 Reputation points

2026-07-20T14:57:52.7266667+00:00

Share -> Email from Adobe Acrobat seems to be working again with the 2606 (Build 20131.20154) July 14th release.
T Ferguson 0 Reputation points

2026-07-30T23:58:22.0066667+00:00

I am having a similar problem.

I would say 8 times out of 10 I can not add simple attachments (eg low file size PDFs) to an email, either by dragging and dropping or by using the attach file option from the ribbon at the top.

When I go to attach the file it shows there at the top of the email with the loading bar, but when the loading bar is complete the attachment disappears.

I am on a Mac running macOS Tahoe Version 26.5.2 and Microsoft Outlook for Mac Version 16.98 (25060824)

Answer 1

Starting with Version 2606, users could no longer attach files to items in on-premises Public Folders (Exchange server), including Public Folder calendar items — both existing and newly created items were affected.

Root cause: Comparing file versions inside the Office16 install folder shows EMSMDB32.DLL was not rebuilt alongside the rest of the package in the affected builds — it stayed on an older sub-build while OUTLOOK.EXE and OLMAPI32.DLL moved forward. This creates an internal version mismatch in the RPC/MAPI provider used specifically for on-premises Exchange connections.

User's image

In every case, the failure correlates directly with EMSMDB32.DLL remaining at 16.0.20131.20044 instead of matching the rest of the package — including in the Current and SemiAnnuel Channel, confirming this affects each channels built from the 20131.x branch (v.2606), not only Monthly Enterprise.

Workaround: Roll back to Version 2605 (build 16.0.20026.20166 or 16.0.20026.20236), where all three files are version-aligned.

We hope Microsoft will do a patch cause we have 10 000 devices, and rollback (uninstall M365 and reinstall june version) is not the best solution...

Answer 2

Philipp Schmid 5

Hi, we got the excat same Issue in the newer Builds and went manually back to 16.0.20026.20182. This fixed crashing while drag and dropping files and Mails into other folders.

Pejman Minooei 20 Reputation points

2026-07-10T13:26:22.81+00:00

Did you find any solution yet? We are still facing this issue with our clients, and even the two most recent updates have not addressed it. The only workaround so far is to enable Cached Exchange Mode on the clients' machines.
Hornblower409 12,265 Reputation points

2026-07-10T20:00:48.58+00:00

@Pejman Minooei said

We are still facing this issue ... workaround so far is to enable Cached Exchange Mode

Thank you for the possible workaround to enable Cached Exchange Mode.

The original post on this issue also said "and other Office applications". Are you seeing the problem in other Office apps (e.g. Word)?

Answer 3

Hi Pejman,

Thank you for your response.

Thank you for trying the solutions I previously provided, including clearing the cache, creating a new Outlook profile, and confirming that the issue is not related to any add-ins. However, the problem still has not been resolved.

I have performed testing across multiple environments and different tenants. On version 2606, I have not been able to reproduce the same behavior.

Although I mentioned this recommendation earlier, I still strongly encourage you to contact Microsoft Technical Support for further investigation. The support team has specialized tools that can collect logs and perform a detailed analysis of your environment. In addition, they can help review your tenant environment and organizational network configuration to identify the root cause of the issue.

If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.

I look forward to continuing the conversation.

Answer 4

Ryan-N 14,850 Microsoft External Staff Moderator

Hi Pejman,

Welcome to the Microsoft Q&A forum.

Thank you very much for taking the time to share such detailed information.

Based on my testing environment using Outlook version 2606, Outlook Classic is still able to attach files normally.

First, please help me clear the Outlook cache and check whether the issue is resolved:

You can refer to the following documentation for guidance on how to clear the Office cache:

Clear the Office cache - Office Add-ins | Microsoft Learn

At the same time, I recommend creating a support ticket with Microsoft Technical Support to report the issue. Once the ticket has been created, a support engineer will proactively contact you and assist with reviewing your tenant environment to identify the root cause of the problem.

If the issue is related to the latest version of the product, the Technical Support team will have the opportunity to capture and investigate the case early, and take the necessary actions to analyze and resolve the issue as quickly as possible

To create a support ticket with Microsoft Technical Support, please refer to the following documentation:

Get support - Microsoft 365 admin | Microsoft Learn

Once again, thank you very much for sharing such detailed and helpful information.

If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.

I look forward to continuing the conversation.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Pejman Minooei 20 Reputation points

2026-07-02T15:04:15.37+00:00

@Ryan-N

The issue is that users cannot attach files at all. When they click Insert > Attach File, the file browse window does not open, so they cannot select files from their local drive, network locations, or OneDrive.

In addition, Outlook may display an "Operation Failed" error when they attempt to attach a file. The only temporary workaround is to completely close and reopen Outlook.

As a mitigation, I rolled affected users back to a previous Outlook version 2605 (Build 20026.20182), and the attachment functionality started working again. This suggests the issue may be related to a recent Outlook/Microsoft 365 Apps update.
Ryan-N 14,850 Reputation points Microsoft External Staff Moderator

2026-07-02T16:55:17.89+00:00
Hi Pejman,

Thank you for sharing additional information.

Based on this error code, after updating to Outlook version 2606, it is possible that the Outlook profile or an add-in is causing a conflict and leading to this issue.

Please help me check the following steps:

Open Outlook version 2606 in Safe Mode to determine whether the issue is being caused by an add-in.

Next, please create a new Outlook profile for the affected user.

This will allow Outlook to re-sync data with the server and help prevent any profile-related conflicts that may be causing the issue.
Pejman Minooei 20 Reputation points

2026-07-02T19:53:52.3833333+00:00

Hi @Ryan-N

I tested Outlook in Safe Mode (outlook.exe /safe), and the issue still occurs, which rules out COM add-ins as the cause.

I also created a brand-new Outlook profile for many of the affected users, and the issue persisted. Therefore, recreating Outlook profiles does not resolve the problem, and it is not feasible to perform this for approximately 100 affected users.

Additional observations:

The issue affects multiple users.

It started only after updating to Outlook Version 2606 (Builds 16.0.20131.20090 and 16.0.20131.20112).

Rolling back to Version 2605 (Build 16.0.20026.20182) immediately resolves the issue.

The same mailbox and the same Outlook profile work normally after the rollback.

Office 2016 users are not affected.

Based on these results, I have ruled out both COM add-ins and Outlook profile corruption. The evidence strongly indicates a regression introduced in Outlook Version 2606 rather than an issue with our environment.
Pejman Minooei 20 Reputation points

2026-07-02T21:39:15.0566667+00:00

Thanks for your advice.

I used the Office Deployment Tool to deploy Outlook using the XML configuration with Channel="MonthlyEnterprise" and Version="16.0.20026.20166". This stable version has worked for us without any issues.

I also opened a ticket with Microsoft to see how their engineers can address the issue.
Ryan-N 14,850 Reputation points Microsoft External Staff Moderator

2026-07-02T22:10:01.6966667+00:00

Hi Pejman,

Thank you for sharing this information.

I’d like to make a note of it so that I can help other users if they encounter a similar issue in the future.

Additionally, if you have any updates regarding the issue or need further assistance while working with the Microsoft support ticket, please don’t hesitate to let me know. I’ll be more than happy to continue assisting you.