In 2010 and 2007 its easy, you just delete a single registry entry. 2013 appears to look at the entry for the default browser and go from that. Deleting those entries would cause lots of other problems. Is there any other way to prevent users from clicking on links? Fearing for their jobs isn't enough so I need some sort of barrier. 

Hi,

The only method I can find to achieve the goal is as below:

1. Press Windows key + R to open the Run command, type regedit and press Enter.

2. In the Registry Editor window, navigate to the following path:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\htmlfile\shell\open\command

3. Rename command key. Such as _command.

4. Restart Outlook. Now, when we click a hyperlink in Outlook, we get the following error message:

"Your organizations policies are preventing us from completing this action for you. For more info, please contact your help desk."

I've tested this in my Outlook 2013, and I haven't found any other problems after modifying the registry.

Regards,

Steve Fan
TechNet Community Support