Confirm the message arrived
Start by saying you received the message and that a person will read it. Reference the ticket number if you have one, so customers can quote it later.
Say when they will hear back
Give a real time, such as within one working day. If you are closed, say when you reopen. A specific promise is more useful than a vague thanks.
Link to the two best articles
Add links to the help articles that answer your most common questions. Some customers will find the answer and not need to wait, which saves them time and you a ticket.
Keep it short and plain
Four to six lines is plenty. Avoid long legal text and marketing in the same email. The goal is reassurance and a next step.
Handle hours and holidays
Change the wording when the team is away so the promised time is true. A reply that says one working day during a holiday week costs you trust.
Review it quarterly
Check the links, the times and the tone every few months. Out-of-date auto-replies are common and quietly irritating.