Out-Of-Office Autoresponders Are Being Sent to the From Address and Not the Reply-To


You receive Out-Of-Office and other Autoresponses to the email address specified in the From Address of a sent email, rather than the Reply-To.




The Reply-To email address is only used when an end-user clicks "reply" on the received email.  Most, if not all, automated responses will almost always go to the From email address. This behavior is out of Marketo's control. It's up to the receiving mail server and mail client whether they choose to Reply-to email address or use the From email address or the return path for automated replies.

The reason behind this is that technical standards require that automated replies only go to the From Address. This is the standards document that those email services are following - https://tools.ietf.org/html/rfc3834 . The behavior is out of Marketo's control

RFC 3834: Recommendations for Automatic Responses to Electronic Mail.
 "In general, automatic responses SHOULD be sent to the Return-Path field if generated after delivery.  If the response is generated prior to delivery, the response SHOULD be sent to the reverse-path from the SMTP MAIL FROM command, or (in a non-SMTP system) to the envelope return address which serves as the destination for non- delivery reports.
 If the response is to be generated after delivery, and there is no Return-Path field in the subject message, there is an implementation or configuration error in the SMTP server that delivered the message or gatewayed the message outside of SMTP.  A Personal or Group responder SHOULD NOT deliver a response to any address other than that in the Return-Path field, even if the Return-Path field is missing. It is better to fix the problem with the mail delivery system than to rely on heuristics to guess the appropriate destination of the response.  Such heuristics have been known to cause problems in the past.
A Service Responder MAY deliver the response to the address(es) from the >From field, or to another address from the request payload, provided this behavior is precisely defined in the specification for that service.  Services responders SHOULD NOT use the Reply-To field for this purpose."