Windows 10 mail app not opening links...

Thanks for following up, Philip. We can try a couple of basic troubleshooting step and see which one helps. Please see methods below for reference:

Method 1: remove and re-add your email account

1. Launch the Mail app.
2. Click the Settings (gear) icon.
3. Click Email & app accounts on the left side
4. Click on the account you want to delete under Email, calendar and contacts on the right side
5. Click manage, and click Delete account.
6. Close and re-launch the Mail app, and add you account once again.

Method 2: Check if Windows Firewall is causing this issue, and add exception to the Mail app

1. Search for Windows firewall via Cortana.
2. Click Allow an app or feature through Windows Firewall.
3. Click Change settings.
4. Search for the Windows Mail app and make sure that it is included on the allowed apps and features by ticking on the checkbox right next to it.
5. Restart your PC.

Keep us updated regarding this issue.