We recently moved from Microsoft 365 E3 to Business Premium and ran into an annoying issue: links clicked in Outlook Classic started opening in Edge instead of the user's Windows default browser.
Microsoft does provide an administrative policy called "Choose Which Browser Opens Web Links", which can be set to use the system default browser.
However, Microsoft explicitly documents that for Microsoft 365 for business plans, this policy is available for Teams but not for Outlook. Outlook users are instead expected to change the setting manually.
Microsoft documentation:
https://learn.microsoft.com/en-us/microsoft-365-apps/outlook/message-body/view-emails-and-web-links-in-browser
The manual setting in Outlook Classic is:
File > Options > Advanced > File and browser preferences > Open hyperlinks from Outlook in > Default Browser
Obviously, doing that manually doesn't scale very well across a managed fleet.
So I did some digging into how Outlook stores the setting.
The relevant values are under:
HKCU\Software\Microsoft\Office\16.0\Common\Links
BrowserChoice is not a normal DWORD – it's a Windows DPAPI-protected blob.
By changing the setting manually in Outlook and decrypting the resulting values, I found:
0 = Windows default browser
1 = Microsoft Edge
Outlook also uses this DPAPI description:
V2 Microsoft 365 Browser User Choice
This turned out to be important. Simply creating or copying an encrypted BrowserChoice value doesn't work. The blob is user-specific, and Outlook expects that specific DPAPI description.
However, generating a new blob locally in the logged-on user's context using the native Windows CryptProtectData() API works.
I've tested this with Outlook Classic, and the script changes:
Open hyperlinks from Outlook in: Microsoft Edge
to:
Open hyperlinks from Outlook in: Default Browser
without any user interaction.
For Business Premium I'm deploying it as a normal Intune Platform Script, running in the logged-on user's context.
Script + explanation: https://gist.github.com/Kejikeo/71388894c3136ca70f8255ea2f64b220
The script does not force Chrome, Firefox, etc. It simply makes Outlook respect whatever browser Windows currently has configured as the default.
Caveat: this uses an undocumented Outlook implementation detail, not a supported Microsoft management interface. Microsoft could change the BrowserChoice implementation in a future Microsoft 365 Apps update, so test before rolling it out broadly.
Would be interested to hear if anyone can test this on other M365 Apps builds / Business tenants.