When processing an Apple device, check the files located in /private/var/mobile/Library WebKit/Databases.
The Databases.db file is a SQLite Database file that contains a listing of databases. This file can include (https) Google Mail and Yahoo Mail. The corresponding file name is listed for each database entry.
The individual files are located in /private/var/mobile/Library/WebKit/Databases https_mail.google.com_0/with filenames similar to 0000000000000001.db . This SQLite database contains a full listing of the mail including messages and full information about each message (to / from / subject / attachments /status (draft/deleted/trash/unread etc.).
Information relating to Facebook and YouTube activities also can be found in these databases.
This can be a gold mine that is overlooked many investigators.