Where are out-of-office (OOO) messages typically delivered?
Summary
What email marketers say9Marketer opinions
Email marketer from NeilPatel.com shares that OOO auto-replies are generally sent to the 'Reply-To' address if specified, otherwise they go to the 'From' address of the original email.
Email marketer from HubSpot details setting up OOO replies and notes that these replies typically route back to the original sender's email address, unless configured otherwise within the specific email client or autoresponder settings.
Email marketer from SuperUser answers that generally, mail is delivered back to the 'From' address. However, it depends on how each system is configured, and sometimes it can be 'Return-Path'.
Email marketer from Mailchimp explains that automated OOO replies usually go to the address specified in the 'Reply-To' field. If that's absent, the response goes to the 'From' address.
Email marketer from Reddit shares that OOO messages sometimes fail to deliver because of strict spam filters on the recipient's side, but should be delivered back to the original sender.
Marketer from Email Geeks mentions they have OOO in the bounce processor because enough organizations send it to the Return Path, meaning the actual sender never sees it.
Marketer from Email Geeks agrees there's no standard, observing Return-Path, From:, and Reply-To: being used for OOO replies.
Email marketer from EmailOnAcid explains that the RFC specifies that the 'Return-Path' is the recipient for any error/bounce messages, but for OOO replies, it usually goes to the 'From' or 'Reply-To' address.
Email marketer from StackOverflow shares that OOO messages can be unpredictable, but generally they should be going back to the 'From' or 'Reply-To' address. Some systems might incorrectly use 'Return-Path.'
What the experts say5Expert opinions
Expert from Email Geeks explains they're intended for humans and human originated email, where the envelope from is the same as the header from, so whatever someone implements “looks fine”, and implementers tend not to go beyond that.
Expert from Email Geeks shares that OOO implementation is client-level and lacks a standard, with clients making different choices.
Expert from Email Geeks explains it's unpredictable where OOO messages are sent, but RFC suggests the worst choice. Expect From or Reply-To. Unsure if Sender is used.
Expert from Word to the Wise explains that auto-replies, including out-of-office messages, are often sent to the address in the `Reply-To` header, or if that's not present, to the `From` address. Some poorly configured systems may send them to the `Return-Path`, which is not ideal.
Expert from Email Geeks confirms that there is no control over where OOO messages will end up, nor their format.
What the documentation says5Technical articles
Documentation from RFC Editor details that 'Return-Path' is technically where automated replies like OOO messages should be sent according to standards. However, this isn't always followed in practice.
Documentation from IONOS confirms that the automatic OOO email is sent back to the original sender's email address. The original sender will be able to see that you are not in the office.
Documentation from Microsoft explains when configuring automatic replies in Outlook, the replies are typically directed back to the original sender. Options might exist for internal vs. external replies.
Documentation from Google explains when configuring automatic replies in Gmail, the reply is sent back to the original sender's email address.
Documentation from University of Washington explains that it expects the OOO email to be routed back to the sender of the email automatically.