I have spent years using different solutions to ‘get rid’ of email address in a development / test / training environment but still wanting to test email functionality so switching off emails wasn’t a viable option.
I have in the past used workflows with hard values inside it to automatically replace any email value with a set value. I then wondered if there was a way that I could do it where I could package it up into a solution to share but, only have people needing to change items in one place rather than in every workflow.
After a few fiddles and some trial and error I developed 2 NON CODE solutions that you can import into your D365 system and then with a few clicks (to update an optionset) you can then feel confidant that no emails will be sent outside of a specified domain.
If you wish to download my solution (its free) you will find it (together with full install instructions) here
If you would like to know a little more on how it technically works and extend it to your own entities and fields look at my blog here