As you can imagine, there are strong dependencies between all of them, meaning that should be no surprise that keeping them at the latest and greatest version (unless unsupported) will contribute to a better experience overall.
Outlook 2013 The latest version of Outlook provides the best and richest experience when used with Exchange Server 2013.
You are all set with adding a delegate but now how do you give them the priviliges?
Now once you add a delegate, you would immediately be asked as to which kind of a delegate is he/she as shown below.
Before putting the blame on the user, ask the Microsoft engineer to see if he can see more of similar deletions (there shouldn’t be any).