[hurstdog]

I have about 2.5 million emails in my work account and it still works really well, as a counter example. (I work at Google, on Gmail backend).

If you've debugged it yourself and can't get to a good resolution (which it looks like you have), please post in our help forums. There are a few people that are dedicated to reading the forum and helping users, and when they hit dead ends for various reasons they'll escalate to the backend team directly and we investigate and fix the account if there is a bug.

Gmail tends to work very well for heavy users, but as with all complex software there are edge cases. Sometimes people fall into those edges and if you escalate through the help forums we'll see a rise in specific types of user escalations and fix whatever bug is causing it.

Hope that helps, -Andrew