Hi @Anonymous,
Have you solved your problem?
Do you want to get the user email address?
Could you please share a bit more about the scenario?
Actually, the information returned by User() function is for the current PowerApps user. It will match the "Account" information that is displayed in the PowerApps players and studio, which can be found outside of any authored apps. This may not match the current user's information in Office 365 or other services including SharePoint user profiles.
As an workaround, I think you should use the Office365Users() to search for this FullName and get user's email address.
First(Office365Users.SearchUser({searchTerm:User().FullName})).Mail