Where does Mac OS X store data files?
Mail files are stored in (hidden) Library sub-directories
mail preferences are in the ‘com.apple.mail.plist’ file, stored in the /Library/Preferences directory
more details can be found at about tech
Contacts are stored in (hidden) Library Application sub-directories
Calendar files are stored in (hidden) Library sub-directories
Music Artwork files (Catalina) are stored in Library sub-directories