Warn a user before opening external Emails (Outlook 2019)

Hello Everyone, 

My name is Rakan, and I need your kind support in something that will help us so much. Recently we have received some complains regarding users failing to pass the phishing test and opening links external to the company, I would like to see if you have a way or a script that Warn the user before opening any External Email from the Email feeds and ask them to make sure before clicking on any link.

Or if you have any other way instead of the disclimer, please be my guest.

Thank you all in advance