When you're a hard-core zero inboxer, you make archive/delete mistakes all the time - that means a lot of undoing. Of course I'm love archive/delete undo to be instant, but I get it, IMAP ain't that fast. But your current solution isn't good enough. Right now in beta 2.6, when I undo an archive, I absolutely no feedback that my action has been received. I've learned to wait about 3 seconds, but initially, I assumed the mac app was broken and I ended up hitting undo ten times, which lead to unwanted results. Instead, just put a placeholder message in the inbox - even if it's unlabeled until you get the operation done. Or something else... but no feedback at all is a real bummer.