Multiple users reported not able to download attachment ( pdf, word, excel ) from Outlook web app

Multiple known issues can prevent downloading or previewing attachments in Outlook on the web (OWA). Use the following checks and fixes, starting with the most likely causes when this affects many users and all browsers.

1. Check if this is an on‑premises Exchange 2016/2019 OWA issue If the environment uses Exchange Server 2016 or 2019 and users open additional mailboxes via Open another mailbox in OWA, a known bug can cause attachment preview/download failures and blank pages.

Symptoms in that scenario:

• After installing or updating to Exchange 2019 CU7 or Exchange 2016 CU18, attachments in an additional mailbox cannot be previewed.
• Users see: “Something went wrong while the document preview was being created. Please try again later.”
• Downloading opens an empty page with a URL beginning https://outlook.office365.com/owa/....

Resolution:

• For Exchange 2019: install Cumulative Update 8 for Exchange Server 2019 or any later CU.
• For Exchange 2016: install Cumulative Update 19 for Exchange Server 2016 or any later CU.

Workarounds until the CU is installed:

• Have users open/download attachments from the additional mailbox using the Outlook desktop client instead of OWA.
• Or use OWA light for the additional mailbox by appending ?layout=light to the mailbox URL, for example:
  • https://owa.contoso.com/owa/******@contoso.com/?layout=light

2. Check for Microsoft Purview DLP–related download blocking If the organization uses Microsoft 365 E5/A5 with Microsoft Purview Data Loss Prevention, a past issue in the DLP file scanner blocked downloads from web apps in all browsers.

Key points:

• Affected period was December 11–14, 2023.
• Downloads from web apps (including OWA) could fail in any browser.
• The root cause was a new DLP feature that did not correctly clean up object references, causing the file scanner to block downloads.

Status and mitigation:

• The affected feature has been automatically disabled on Windows devices; the issue should now be resolved.
• A mitigation disabled scanning for files saved to the Downloads folder path. If users still see issues when saving to Downloads, restarting the Windows device ensures the fix is applied.
• Admins can verify mitigation by checking the registry key:
  • Computer\HKEY_LOCAL_MACHINE\Software\Microsoft\Windows Advanced Threat Protection\Status
  • ConfigurationVersion should be 10.8699.icm450350786.2023.12.14.01-2D153B40CE0194E989F549365C4CD2E400CB1005E8D404C7EBAC83CE3DF9FE0E.

3. Check Defender for Cloud Apps session policies blocking downloads If Defender for Cloud Apps session controls are used to block downloads for OWA, previewing or printing some files (especially PDFs) can also be blocked because the app internally initiates a download.

Behavior:

• Users may see a “Download blocked” message when trying to preview/print.

Fix (Exchange Online admin):

1. Install the Exchange Online PowerShell module.
2. Connect to Exchange Online PowerShell.
3. Update the OWA mailbox policy to disable direct file access (so preview works while downloads remain blocked by the session policy):

      Set-OwaMailboxPolicy -Identity OwaMailboxPolicy-Default \
        -DirectFileAccessOnPrivateComputersEnabled $false \
        -DirectFileAccessOnPublicComputersEnabled $false
   

4. If multiple OWA mailbox policies exist, update each one applied to affected users.
5. Test again in OWA with a PDF and the session policy configured to block downloads; the Download option should be removed and preview should work.
6. Confirm file types are not blocked by OWA If only certain attachment types fail, verify whether they are blocked by Outlook on the web.

• OWA allows many common file types (for example, .docx, .xlsx, .pptx, .pdf, .png, .mp3) by default.
• It blocks many potentially dangerous types (for example, .exe, .bat, .cmd, .js, .vbs, .ps1, .msi, .reg, and others). Blocked types cannot be opened or downloaded.

If the failing attachments are among the blocked extensions, this is by design and not a browser issue.

5. If issue is browser‑specific or profile‑specific If only some users or browsers are affected and Exchange/DLP/Defender policies are ruled out, corrupted browser settings can interfere with downloads.

A known fix for OWA download errors in Chrome is:

• Reset Chrome settings to their original defaults.
• Reset Chrome services to defaults.

After these resets, OWA attachment downloads started working again for the affected user.

Apply similar troubleshooting in Edge (reset settings, clear cache) if the problem is limited to certain profiles or machines.

References:

• Attachments can’t be downloaded or previewed from Outlook Web App
• KB5034596: You might have been unable to download files from web apps using any web browser
• Public attachment handling in Exchange Online
• Can't open or view attachments in Outlook on the web
• Troubleshooting access and session controls for end-users
• Troubleshoot attachment problems in Outlook for Windows
• Error message when trying to download attachments from OWA 365 - Microsoft Q&A