It comes back after 12 hours or so, then takes a while to deliver most of the missed messages. I found this out by breaking a recurring task on a site of mine,

It comes back after 12 hours or so, then takes a while to deliver most of the missed messages. I found this out by breaking a recurring task on a site of mine, which had error logging set to email me. But the task was spinning through a a list of things to process, and throwing/emailing for each item (to a gmail label I only check occasionally). Then trying the whole thing again on the same (now somewhat bigger) list a minute later. It got up to a few thousand mails per minute before Google said enough. I happened to notice it right away and put the fix in place, but it still took the better part of a day for things to percolate through and go back to normal. I don't think I missed any real mails from real people. They just arrived a day late.