How to Automatically Delete Older Messages in Gmail

The Trash and the Spam folders in your Gmail have a unique auto-purge property and old email messages belonging to either of these labels are automatically deleted after a fixed period of time (30 days to be precise).

How to Enable Auto-Purging in Gmail

You can’t enable auto-purging in Gmail for any particular label but there’s a simple Google Script that will bring this missing functionality to your Gmail. The script will basically monitor messages belonging to a particular folder /label in Gmail and purge those that have exceed the retention time.
Here’s how you can get auto-purge to work inside your Gmail:

1. Open Google Script and choose File -> Make a copy to copy it into your Google Drive.
2. Set the value of GMAIL_LABEL to the label that you wish to auto-purge and PURGE_AFTER are the number of days for which you to retain a message in 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.
4. 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. If you need to disable auto-purging later, just open the same script in your Google Drive and choose Run -> Uninstall.