[German]Microsoft seems to allow links in mails that are displayed via mail app to be opened in any browser. This is a fundamental change, because Microsoft announced earlier this year, that such links will be opened in Edge browser only.
Microsoft has announced Windows 10 Insider Preview Build 17623 in Windows Blog, that the Windows Mail app will open links only in Microsoft Edge:
For Windows Insiders in the Skip Ahead ring, we will begin testing a change where links clicked on within the Windows Mail app will open in Microsoft Edge, which provides the best, most secure and consistent experience on Windows 10 and across your devices. With built-in features for reading, note-taking, Cortana integration, and easy access to services such as SharePoint and OneDrive, Microsoft Edge enables you to be more productive, organized and creative without sacrificing your battery life or security. As always, we look forward to feedback from our WIP community.
Now it seems, that the feedback wasn’t too overwhelming. Now italien web site postet a screenshot of an early Mail app update, that showns an option to change that association (see also here).
(Options in Mail app)
The screenshot shows an option within the mail app settings that can be used to specify whether or not mail links should be opened in Microsoft Edge. With Edge option disabled, links in Windows Mail app should reopen in the default browser of the operating system.