How this Mbox backup functionality works

Why are you asking in a Thunderbird forum how a gmail mbox backup works? Do you go to a Toyota forum to ask how your Mazda works?

Basically you will get whatever GMail has appropriate labels on. The vast majority of your mail in the mbox will be in the all mail folder, where gmail keep, well, all your mail. If you did not select it as an option when you got your mbox file you might find you mail very much slimmed down.

I did asked to the Google support regarding gmail mbox backup but they don't provide any support on mbox and as per them I raised a query over here

sudhakarbhagat said

I did asked to the Google support regarding gmail mbox backup but they don't provide any support on mbox and as per them I raised a query over here

because Thunderbird uses the mbox format to natively store mails, it odes not make Thunderbird support a defacto support for Googles offerings. They offer the file, they need to explain what is in it. When they start sending a cheque to pay for providing support to Google products, then I will look at offering support for them.

For information on the mbox format generally I suggest you look to wikipedia. https://en.wikipedia.org/wiki/Mbox