Gmail Proof or received emails

Hello,
I know that this will sounds stupid. But I have received an email from client that he wants to create some kind of proof document of received emails in Gmail for certain period of time. Is something like that possible? I have tried to find it on Google. But no luck there. Thanks and please don't roast me.

If I understood it correctly, then this might help.

https://chrome.google.com/webstore/detail/export-emails-to-google-s/ibpbagbedfnlepijbnjeanihpoohkocm
It is basically a extension that will let you export emails into a Google sheet.

You can just screenshot it. I think he just wanted receipt.