As described in this question.
Both the Vacation Responder and using a filter to send a Canned Response send the response the Return-Path field of the email, not the From field. Please don't tell me this isn't the standard, I know that. I need a workaround!
I am trying to set up an SMS auto-responder from Google Voice. So I set Google Voice to forward texts to Gmail. But in Gmail there is no way to auto-reply to texts in the same message—it sends a new separate message using the Return-Path address. So, Google Voice does not receive the message because the Return-Path address is a bounce address. So Google Voice does not receive and forward the text back properly, so the auto-reply does not work.
Can anyone help please? It's very frustrating that there is no way to do this.