This accords with my experience - in fact, I'm amazed that the figure isn't higher across the board.

Email is the boring plumbing of the Internet but so totally essential it seems remarkable that more effort is not put in to supporting it properly so that such problems do not arise. I don't mean management of the software and hardware, removal of spam, virus protection etc- that part I take as a given. I mean the real management, in which managers listen to what the people using their machines need, proactively anticipate their wants, monitor how they are doing. A free email account from Google can run rings round what most organisations can provide, in reliability, security, spam protections, capacity, speed, accounting, manageability. If corporate email could serve needs better then people would be less inclined to bypass it, but the investment needed if networking departments were to listen and act on what people want and need would be huge, given decades of underinvestment. Necessary, though.