All of this stuff is useful for a user migration to a clean OS install.
Mail files and preferences.
The actual mail files are located here:
And the mail application preferences are located here:
Your Safari bookmarks are here:
Export your address book like this:
File -> Export -> Address Book Archive
Reimport them by double-clicking the file and having that previous export overwrite what you already have in place.
Or you can copy the full address book directory from here:
Export your iTunes playlists like this:
File -> Library -> Export Playlist
The reimport the playlists like this:
File -> Library -> Import Playlist
Or you can copy the full iTunes music directory from here: