I ran a nonprofit organization staffed entirely be volunteers (I was one). After one too many people incensed that we did not follow up to their emails within two hours, we had to include an OOO message that said we were a volunteer organization, and any request may take up to two weeks to process. Please email again if you have not heard from us by then.
Earlier this year, British comedian Steve Coogan underscored a growing trend to rethink the OOO when he used it not to advertise his own absence, but rather the return to our screens of his blazer-clad alter ego, hapless media personality Alan Partridge. Written in the broadcaster’s inimitable voice, it had stern words for anyone who dared email him: “I’m not in the office so both cannot and will not respond to your email,” it began. “If your email is urgent, perhaps you should have tried calling instead. The very fact you were content to type out your query long hand and settle back to wait for a reply suggests you can wait, even if you’ve put a red exclamation next to your email to make it stand out in my inbox. Won’t wash with me, that.”

It’s so much easier for everyone to have an OoO that says “I’m gone- please contact PaperClipSortingTeam ‘at’ spacelyspacesprockets for help while I’m out.
I typically say “thanks for your message, I’m out until blah date, with periodic access to email” or no access depending. I list contacts who are willing to pitch in if necessary, and list the day AFTER my return that I’ll be able to address messages.