I’d probably say something like “I am unavailable until X date. Please contact [colleague] or [colleague] if you need assistance. Thanks!”
I recently described myself as being “out of the virtual office.” Away from the virtual office” would probably have been even more precise. I think whatever you say, people will understand what you mean.

If you have a corporate email account at work, the chances are you'll also have some kind of setting that enables you to tell people when you're on holiday or out on the office on business. But what if you don't? Or just want to set up an email auto reply on your Mac at home?
Hoo boy, have I got some PTSD from Old Job about out of office autoreplies. Exboss was such a stickler for them and actually enforced her expectations as official policy. Meaning if you didn’t do it to her exact specs, she’d call you back to the office to do it (which no one did) and read you the riot act afterwards while threatening to write you up for insubordination. She demanded them any time that we were away from our desk for longer than 30 minutes and for anything other than a meeting. So training in the conference room down the hall, a work lunch with teammates, leaving an hour early for an appointment, arriving late for an appointment, even working from home, all required OOO alerts.