Automated email messages generate a 70.5% higher open rate and a 152% higher click-through rate than standard marketing messages. Briefing what would be the next step of action gives customers transparent information.
I hate when senders ignore the instructions in my OOO message. Usually, my message is something simple like: “I am out [Dates], returning to the office [Date]. Please contact Jane (jane’s email address) in my absence. General [department] questions may be sent to [general dept email address].” To me that says if you are sending me anything then I won’t see it until I return. If you have something you need to be resolved right away, you can contact Jane or send it to our department inbox (where it should be going anyway).

It was very inefficient but I was making $3 above minimum wage and it was air conditioned. So no argument from me. They took me back for the winter break and would have had me every other summer except I did internships, so I guess I didn’t do too badly.
Voice mail is a strictly worse medium than almost any alternative. You don’t get the opportunity to converse and ask questions back and forth like you do with a phone call; you can’t extract information efficiently from the message like you can with an email (the old “ugh, I have to listen to this entire message over again just to check one thing he said at the end” scenario).