Hyperlink from outlook not able to open

Question

When I attached a hyperlink from the shared drive on a documents and send it to my colleagues they are not able to open the hyperlink. It will come out with a warning security notice and when press yes it will inform that the location or address cannot be found. Later I found out that it is because of the folder that contain the files has a # that prevent the documents from opening. Previously there is no such issue when opening the hyperlink even if the folder has a #. Did microsoft do any updates?

Answer 1

Hi Adrian,

Yes — this issue is increasingly common with recent Microsoft security hardening updates affecting links to shared drives or network folders, especially when special characters like # are present.

Here’s what’s likely happening:

1. Outlook’s Protected View and newer security baselines are stricter with UNC/shared path links that contain unsupported characters (like #, %, or &).
2. This behavior changed with recent Office security updates and Windows Defender SmartScreen policies.
3. Some updates now block access to links with characters interpreted as potentially unsafe in URLs.

✅ What you can try:

• Avoid special characters like # in folder/file names (as you've discovered).
• Ask your IT admin to review GPOs or policies related to:
  • Office File Validation
  • Microsoft Defender Application Guard
  • Outlook Attachment Manager
• If this is internal and safe, you can allow specific UNC paths through registry policies (HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Office\16.0\Common\Security\Trusted Locations)

Let me know if you’d like exact steps depending on your version of Office.

—

Nicolas Bourdeau – Wintive

Microsoft 365 Consultant | Exchange & Teams

🌐 https://www.wintive.com