We all get them. When my weekly newsletter goes out, I get dozens. It's the "Your email is important to me, but I'm out of the office until ..." If the customer is lucky, there may be a requirement for them to take another step if they really need help, with "Please email my assistant, George, at george@ouremail.com if you need immediate assistance."
First, I'm a customer, so my email BETTER be important to you, so telling me is not necessary.

Second, if my email wasn't important to me in the first place, I probably wouldn't have sent it. So, why don't you do an automatic temporary forwarding of your email to George? If your personal email is mixed with your business, then this might not be a good idea, but you should try to figure out a way to get this done without requiring your customer to take extra action. At the very least, give them a link to George's email address and have them forward their email to him so they don't have to type it again.

This practice wastes Internet resources, with many millions of these going out every day. They clutter our customers' email inboxes, and pretty much tells them that they're not going to be taken care of while we're out of pocket. While many may disagree, I would monitor my email once or twice a day while away, and at least selectively forward those who need attention to my assistant. And, I'd do it without letting them know it's happening. George can email them, take care of their request, and let them know that you're out of pocket so he's handling things.