The one time I ran out of quota in Gmail, because Google backup for MacOS has a serious bug, I did not receive the notice because the same batch job that disables delivery for your account is the one that sends you the email. I didn’t get the message until a week later when I figured it out and deleted some photos. Pretty dumb.

Also, Gmail delivers an in-band message about your quota, but not in Inbox, Inbox for iOS, nor the Gmail app for iOS nor Gmail for mobile web. ONLY Gmail classic for desktop web. So I didn’t get those banners, either.

In other words I still find this quota system difficult to use despite the fact that I was the tech lead of Gmail delivery SRE for years.