Even that would be hard to use in real life, as an "out of office message" does not mean that their colleagues can't easily reach them. If you're some outsider

Even that would be hard to use in real life, as an "out of office message" does not mean that their colleagues can't easily reach them. If you're some outsider you don't know if that person is really unreachable or if their colleagues can easily reach them on Slack/send them a text/whatever if they have some important question. And if you are internal/close enough to know their time off plans and that they're going backpacking in the Canadian Arctic, you didn't need the message to tell you they're out of office.