I will return with a glowing tan on [insert date] and respond promptly to all emails. If your request is time sensitive, please email [insert name] at [insert email].
Leaving an email without a responder can appear unprofessional, lose potential business and, worst of all, make you look like Scrooge!

I used to work with someone who had a message telling people she only checked her email twice a day. You pretty much needed to call her if you needed anything outside of those times. (She worked in a remote office.) I think she had read one of those books on efficiency that recommended scheduled email time. But there were problems with this: 4. My department often had to email attachments or text to illustrate our questions/concerns. And we were on deadlines. Reading a page of text over the phone was not an efficient use of anyone’s time 5. She did outreach & was often out of the office on site visits, trainings, or travel to these places, but never ever set her OOO for these, because she was “working.” However, she was effectively not available to read emails from other staff until after hours on those days.
That’s it. That’s all. Simple and to the point, this message will let people know that you can’t respond to messages.