How to Export Your Emails from Gmail as mbox Files
To download a copy of the messages in your Gmail account in the mbox file format:
How a Gmail Archive Works
When an archive is created by using one of these options, Google emails you a link to the archive location. Depending on the amount of information in your account, this process could take a few minutes or several hours. Many get the link to the archive the same day.
To download only certain messages, select All Mail.Check Select Labels.Check the labels that tag the emails you want to download.
The email storage format used to organize email messages is a single text file called an mbox file. The mbox file saves messages in a concentrated format in which each message is stored after another, starting with the From header. This format was originally used by Unix hosts but is now supported by other email applications, including Outlook and Apple Mail.