I have gotten weird pushback on this that people are offended that I would say I am out for religious observance, as if it somehow implies that my reason for being out of the office is more important (or inviolable) than theirs. I don’t even know what to do with that.
There’s a grim, apologetic vibe to these messages — I’m sorry I’m taking time for myself but I’ll try to check in on occasion! They’re a vivid reflection of a work culture that valorizes constant productivity and the near-total overlap of work and life. But they’re also do a terrible job of what they’re intended to do, e.g., set realistic expectations for both sender and recipient. A vague OOO message traps both parties in an uncomfortable liminal space where both productivity and rest go to die. The original sender is left unsure if they’ll be getting a timely response or a whether the email will go ignored for a time or forever. The original recipient has taken what is a rock solid excuse (time off) and cheapened it, offering a backdoor for email guilt to creep in.

Read our guide to setting up email on a Mac, iPhone and iPad here. Plus how to send email attachments in Mail on iPhone.
In most cases, the voice of your out of office message should be similar to the voice you’re using while communicating with clients. If you’re usually formal, replying with a joke could be jarring — and vice versa. Your mileage may vary, but keep that in mind before setting up an automatic reply.