What is Gmail?
Gmail is a free (gratis), advertising-supported email service provided by Google. Users may access Gmail as secure webmail, as well as via POP3 or IMAP4 protocols.
How to Download/Take Backup of Full Gmail Account?
Google has started a service called “Takeout”. It allows you to backup any Google Products you are using. Google allows you to take a MBOX copy of your Gmail archive. You would need to generate it from “https://www.google.com/settings/takeout/”.
Once the generation is done, you can download the backup and load it in any MBOX environment.