A validation rule for deletes
You can implement delete rules like validation rules on your Contact records using formula syntax to decide on when deletes are allowed and what the messages to your users should be.
Define the error message with a formula
Using a formula with any contact (or lookup relationship to contact) you can create a totally custom rule set that is crystal clear for users when they are blocked from deleting a record.
One configuration for classic and lightning
The same function will work in lightning, classic, or any interface. This can be used to ensure that Outlook Sync doesn't delete important contacts for instance.
We wanted to make a simple solution to a simple problem, and that's what we did. We depend on this package with many of our consulting clients and has been a huge asset.