Automatically Deletes older message in Gmail inbox
How to Enable Auto Purging in Gmail
Here’s how you can get auto-purge to work inside your Gmail:
3) Go to Run ==> Initialize and grant the necessary permissions. This is your personal script and nobody else will ever have access to your data. it is totally secure.
4) To install it Go to Run ==> Install to install the auto-purge script.
That’s it. Exit the Google Script and it will continuously monitor that particular Gmail label in the background.