OWA service incident -user unable to download attachment Outlook web app error

Question

Multiple users reported they are not able to download attachment on outlook web

Answer 1

There is now a Microsoft Service Advisory for this issue.

Users may be unable to download or open email attachments in Outlook on the web
https://admin.cloud.microsoft/?#/servicehealth/:/alerts/EX1275040

Issue ID: EX1275040. Affected services: Exchange Online. Status: Service degradation. Issue type: Advisory. Start time: Apr 9, 2026, 6:48 AM CDT. Scope of impact: Some users attempting to download or open email attachments in Outlook on the web are impacted. This information may be updated as our investigation continues.

Current status Apr 14, 2026, 3:09 PM CDT

Our HAR trace analysis has focused our investigation to a token failure that we believe could be preventing the opening of email attachments for users in Outlook on the web. We're further analyzing the isolated failure to confirm our findings and so our next troubleshooting steps for remediating the impact can be determined.

[Not Official - Based on the reports I have seen, if an account is hoarked then you will see the same problem using both Outlook Web and New Outlook for Windows]

Update Friday, April 17, 2026, at 5:00 PM UTC

• Root cause: An authentication issue on a portion of Outlook on the web infrastructure responsible for downloading and opening attachments was resulting in impact.
• Next steps: We're reviewing the affected portion of Outlook on the web infrastructure to determine how the authentication issue was introduced, so that we can prevent similar instances of impact from occurring in the future.
• This is the final update for the event.

Answer 2

Hi @RobE

Regarding your issue, this behavior with Outlook on the web where email attachments can’t be downloaded or opened has been recognized as a service-side issue affecting some users. 

Currently, the issue is still under investigation, and the service team is actively working to identify the root cause and apply a fix. Not all users are impacted, and other Outlook or Exchange features may continue to work normally. 

At this time, there isn’t a client-side setting or local troubleshooting step that can fully resolve it right now. The best approach is to: 

• Monitor the Microsoft 365 Service Health updates in the admin center. 
• 
• Use an alternative client (such as Outlook desktop or mobile) as a temporary workaround, if possible 

I understand the inconvenience this can cause and appreciate your patience while the issue continues to be reviewed. 

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Answer 3

Based on the described behavior (multiple users unable to download attachments in Outlook on the web), use the following checks and fixes depending on the Exchange/Outlook environment.

1. Check for recent Exchange Server updates (on‑premises)

• If using Exchange Server 2019 or 2016 and the issue started after installing the March 2024 Security Update, this matches the known problem where download domains stop working and:
  • Inline images no longer display in OWA.
  • Attachments cannot be downloaded in OWA.
• Resolution: Install the hotfix update KB5037224 for Exchange Server 2019/2016 as documented in the “Download domains not working after installing the March 2024 SU” article.

2. Verify download domains and special alias patterns (Exchange 2019)

• If Download Domains are configured and affected users have aliases beginning with oma*, and inline images or text attachments fail (broken image icon or “page not found” when downloading), this matches the “Inline images and text attachments are not visible in OWA” issue.
• Resolution: Install Cumulative Update 15 for Exchange Server 2019 or a later cumulative update.

3. Check for known OWA attachment issues after specific CUs (Exchange 2019/2016)

• If using Exchange Server 2019 CU7 or Exchange Server 2016 CU18 and users are opening an additional mailbox via “Open another mailbox” in OWA, then:
  • Attachment preview shows: “Something went wrong while the document preview was being created. Please try again later.”
  • Downloading an attachment opens an empty page with a URL starting https://outlook.office365.com/owa/....
• Resolution:
  • For Exchange 2019: Install CU8 or later.
  • For Exchange 2016: Install CU19 or later.
• Workarounds until updated:
  • Use the Outlook desktop client to open/download attachments from additional mailboxes.
  • Or access the additional mailbox using OWA light by appending ?layout=light to the mailbox URL.

4. Confirm message/attachment size limits are not exceeded

• If users see errors like:
  • “The following files couldn't be attached: Filename. Please try again later.”
  • “The following files weren't attached because adding them would cause the message to exceed the maximum size limit of 10 MB: filename.”
• Cause: The attachment exceeds the configured message size limit (default 10 MB in the documented scenario).
• Action: Verify and, if needed, increase the message size/attachment limits in Exchange/tenant configuration, or instruct users to reduce/compress files before sending.

5. Browser‑side troubleshooting (OWA 365 / Outlook on the web)

• If this is Microsoft 365 (Exchange Online) and only certain browsers/clients are affected (for example, Chrome on macOS) and the error is generic such as “Error. The request could not be completed. Try again in a little while.” for all attachment types:
  • Reset the browser profile/settings:
    • In Chrome: Settings → Reset Settings → Restore settings to their original defaults → Reset settings.
    • Also reset Chrome Services: Services → Service Settings → Restore Defaults.
  • After reset, test downloading attachments again.

6. If the issue persists for multiple users/tenants

• For Microsoft 365 tenants where the above steps do not apply or resolve the issue, raise a support ticket via the Microsoft 365 admin center so engineering can review backend logs for OWA and attachment handling.

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References:

• Download domains not working after installing the March 2024 SU
• Inline images and text attachments are not visible in OWA
• Attachments can’t be downloaded or previewed from Outlook Web App
• Error when adding a large attachment in Outlook on the web
• You cannot add attachments, delete or move many email messages in bulk in Outlook Web App
• Can't open or view attachments in Outlook on the web
• Error message when trying to download attachments from OWA 365 - Microsoft Q&A