FTFA: issues a reply to the sender that the person is out of the office and that the email will be deleted, while also offering the contact information of another employee for pressing matters.
the program — which is optional — has gone down well with the company’s German employees
Seriously, the idea is that you get to actually take a vacation and let someone else handle the load while you're away. That way, you're not coming back to work with twice the workload as when you left. For many companies, if you take a vacation, no one covers you. The work just piles up. It makes it hard to relax knowing that you've got a mountain of work to return to. No one is taking away "Out of Office" messages or breaking them for people who want to use them.
I've seen several comments here saying "Well, I'm just CC'ing people who need to be kept in the loop!" Ok, I get that. If it's that important, why don't you just wait until they get back and give them a short briefing? If it's not that important, why did you bother sending it in the first place?
I, for one, applaud the effort to push back against the anti-vacation, anti-personal time culture.