Try this.

Right-click on your desktop, goto "New" and choose "shortcut".

In the create shortcut dialog, browser to opera.exe in Opera's install folder. You can find the install folder path by going to the URL opera://about.

Click Next.

Name the shortcut Opera as Chrome and click finish.

Then, right-click on the "Opera as Chrome" shortcut, goto "properties" and edit the target field.

In the target field, after the command to opera.exe, add a space and then:

so that it looks like:

for example.

Then, click apply and ok out.

Then, with Opera closed, start Opera with that "Opera as Chrome" shortcut and try things out.

If that doesn't work:

Download the offline package of Opera from https://www.opera.com/download.

Goto the URL opera://about and take note of the install path.

Uninstall Opera via programs and features while choosing to keep your data (if you want to keep your data).

After Opera is uninstalled, delete the install folder if it still remains.

Launch the offline package installer and click "options". Set the "install path" to "C:\Program Files\Opera", set "install for" to "all users", uncheck "import data from default browser", check "Make Opera the default browser" and install.

Then go back to "Default Programs" in Windows and make sure Opera has all its defaults.

Then it should just work. But, to test that things are correct, open a command prompt and enter this command:

It should then open in Opera. If you get asked what app should open the URL, selected "always use this app" and select Opera.

Try the same thing with:

If those both open in Opera, then Opera is configured correctly. If Opera still doesn't open from Outlook, I'd blame Outlook.

You can also go into Default Programs and choose to set a default by file type and choose the https and http protocols and set them to Opera.