This article lets you to define how you can export Emails from Gmail as MBOX Files. Using this method, all your items and messages of your Gmail account are easily available for Download through POP and IMAP.
Read more here:- https://medium.com/@bobmaria57/how-do-i-export-emails-from-gmail-as-mbox-files-and-restore-them-back-to-gmail-account-f6d4f589da75