Here are some suggestions for what you should always include in your auto-reply emails when you are out of the office:
Here are some do's and don’ts for crafting an effective outgoing message, along with some out-of-office message examples: The exact dates of your time off — If you are simply reactivating the message you used during your last time away, make sure you change the dates, and double-check to ensure they’re right. The reason for your absence — Colleagues might still attempt to get in touch with you if they think you’ll be checking in. They’ll be less likely to try to contact you if they know you’re taking personal or vacation time. The people who can help while you’re out — Provide their names, phone numbers and email addresses. If you handle multiple areas, specify each person’s area of expertise so colleagues and clients know exactly where to go for assistance. What to avoid in automatic replies

Just say you’re away from your desk! Or if you’re out for more than a day, just say you’re “away” until XYZ date.
I did something similar the second time I took maternity leave, actually. I didn’t explicitly say, “I will delete all emails,” but instead I shared my backups’ contact info and invited people to contact me again when I was back from leave.