Have you tried deleting a very large number of messages? I am talking about > 100,000. I once needed to clean up > million messages and it was rather challenging even utilizing Google's scripting. Batching ( within Google's recommended parameters ) would periodically fail. Triggers would not run. etc.
1. Move all the messages to a folder.
2. Then delete that folder.
I took several days deleting a few hundred thousand messages, "Select all", "delete". Each time it would remove 1000-10,000 messages and leave the rest. Was a real pain.
1. Get current time, increase the time by 5 minutes and find the 5 minute mark after that.
2. Register itself to run the time determined in (1).
3. Fetch a batch of 9000 ids matching the filter.
4. Delete the batch
This script would comfortably run for days cleaning out the inbox until it would hit some weird message that looked nearly identical to the messages around it and bomb(!?). Running it by hand would bomb at which point script won't be able to continue to execute. Deleting a message by hand would work. Running the script again after the manual deletion would work.
although I tried deleting for one or two years at a time