I wrote a small script, which can automatically clean Your GMail Inbox.
Update is now available via Scriptgalerie.
Select the label(s) You want to be cleaned
regularily. All mails / threads which are older then the configured age
are moved automatically to Your trash.
Open a new new Google Spreadsheet:
and go to Tools and Scriptgalerie.
Search for GMail Cleanup, install it and grant authorization.
Opent the Scriptmanager via the Tools.
Select the onOpen function and click execute, the config screen should appear.
Set Your options, click Submit and Close.
Go to the Scripteditor, Triggers menu and choose "current scripts triggers". Click the link to set up a new trigger, choosing the "moveToTrash" function, a "time-driven" event, "day timer," and then for example "midnight to 1am." Click save and you are done.
You can also setup an email alert if something goes wrong.
Via Scriptmanager, execute the function moveToTrash.
You can view and edit the code, if You installed it.
To view it,open Your spreadsheet and go to Tools and select Scripteditor.
A new Tab with the script source will be opened.
You can deinstall it via the Scripteditor.
Select on the left side the top level GMail Cleanup Script and choose Menu, delete.