Summary
The delivery of out-of-office (OOO) messages is inconsistent and depends on how the email system is configured. While RFC standards suggest that automated replies should be sent to the 'Return-Path,' this is not commonly followed in practice. Many email platforms, such as Outlook and Gmail, typically send OOO replies back to the original sender's email address. If the 'Reply-To' address is specified, the OOO message may be sent there instead of the 'From' address. Implementation is also client-level and lacks universal standards, leading to different choices by different clients. Additionally, some systems might incorrectly use the 'Return-Path,' and spam filters can sometimes block the delivery of OOO messages.
Key findings
- Inconsistent Delivery: The delivery of OOO messages is unpredictable due to variations in email system configurations.
- RFC Standard Not Followed: RFC standards suggest sending automated replies to the 'Return-Path,' but this is often ignored.
- Common Practice: Many email platforms, like Outlook and Gmail, send OOO replies to the original sender.
- Reply-To Priority: If a 'Reply-To' address is specified, OOO messages may be sent there instead of the 'From' address.
- Client-Level Implementation: OOO functionality is implemented at the client level, leading to different choices by different clients, without universal standards.
- Return-Path Misuse: Some systems incorrectly use the 'Return-Path' for OOO messages.
- Spam Filter Impact: Spam filters can sometimes prevent the delivery of OOO messages.
Key considerations
- Lack of Control: There is no guarantee where an OOO message will be delivered, as it depends on the recipient's email system configuration.
- Header Importance: The 'Reply-To' and 'From' addresses in the email header play a significant role in determining the delivery destination.
- System Awareness: Be aware that different email clients and servers may handle OOO replies differently.
- Spam Filter Monitoring: Monitor spam filters to ensure that legitimate OOO messages are not blocked.
- Configuration Verification: Verify the configuration of your email system to understand how OOO replies are handled and ensure they are being delivered correctly.
- Fallback Strategy: If using a no-reply From address, provide contact information so the OOO doesn't disappear.
What email marketers say
9 marketer opinions
Out-of-office (OOO) message delivery is inconsistent and varies depending on the email system's configuration. While the RFC standards technically suggest the 'Return-Path', in practice, OOO replies are most commonly sent to the 'Reply-To' address (if available) or the 'From' address of the original email. Some systems may incorrectly use the 'Return-Path', and spam filters can also impact deliverability. Ultimately, there is no guarantee where an OOO message will be delivered.
Key opinions
- RFC Inconsistency: Although RFC standards suggest 'Return-Path', this is not widely followed for OOO messages.
- Preferred Destinations: 'Reply-To' and 'From' addresses are the most common destinations for OOO replies.
- System Variation: Delivery behavior is heavily dependent on the specific email system and its configuration.
- Delivery Issues: Spam filters can sometimes prevent OOO messages from being delivered.
- No Standard: There's no single, universally adopted standard for OOO message delivery.
Key considerations
- Unpredictability: You cannot guarantee the delivery destination of an OOO message.
- Header Importance: The presence and accuracy of 'Reply-To' and 'From' headers play a crucial role.
- System Configuration: Be aware that different email clients and servers may handle OOO replies differently.
- Spam Filtering: Ensure your email practices minimize the chances of OOO messages being caught by spam filters.
- Bounce Processing: Some orgs send it to the Return Path, but that means the actual sender never sees it.
Marketer view
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.
3 Feb 2025 - NeilPatel.com
Marketer view
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.
12 Jul 2021 - HubSpot
What the experts say
5 expert opinions
Out-of-office (OOO) message delivery is unpredictable due to a lack of standardization and client-level implementation variations. While some systems send replies to the 'Reply-To' or 'From' address, others may incorrectly use the 'Return-Path'. This inconsistency means there's no guarantee where an OOO message will end up, and its format is also uncontrollable. OOO messages are primarily designed for human-to-human communication, leading to a relaxed approach in their implementation.
Key opinions
- Unpredictable Delivery: The delivery destination of OOO messages is inconsistent and unpredictable.
- Lack of Standardization: OOO implementation lacks a universal standard, varying across different email clients.
- Client-Level Implementation: OOO functionality is implemented at the client level, leading to diverse choices.
- Header-Based Routing: 'Reply-To' and 'From' headers are often used to determine the delivery address, but this isn't always consistent.
- Intended Use: OOO messages are primarily designed for human interaction, influencing their implementation approach.
Key considerations
- No Control: You have no control over where OOO messages will ultimately be delivered or their format.
- System Variations: Be aware of the potential for different email systems to handle OOO replies in unique ways.
- Human Focus: The focus on human-to-human communication means strict adherence to technical standards may be lacking.
- Return-Path Issues: Avoid relying on the 'Return-Path' for OOO delivery, as it may not be consistently used.
- Best Practice: Ensure a Reply-To address is configured when sending emails in case the From address is not monitored.
Expert view
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.
10 Oct 2022 - Email Geeks
Expert view
Expert from Email Geeks shares that OOO implementation is client-level and lacks a standard, with clients making different choices.
6 Sep 2024 - Email Geeks
What the documentation says
5 technical articles
According to email standards (RFC), automated replies like out-of-office (OOO) messages *should* technically be sent to the 'Return-Path'. However, in practice, popular email platforms like Outlook and Gmail typically direct OOO replies back to the original sender of the email. University of Washington and IONOS documentation confirms that OOO is sent back to the original senders.
Key findings
- RFC vs. Implementation: Email standards (RFC) suggest using 'Return-Path', but most email platforms deviate from this.
- Outlook Routing: Microsoft Outlook routes OOO replies back to the original sender, offering options for internal vs. external replies.
- Gmail Routing: Google's Gmail sends automatic OOO replies to the original sender's email address.
- University Expectation: The University of Washington IT guidance confirms it expects the OOO email to be routed back to the sender.
- IONOS Confirmation: IONOS confirms that the OOO email is sent back to the original sender's address.
Key considerations
- Practical Implementation: Focus on how email platforms like Outlook and Gmail actually handle OOO messages rather than solely relying on the RFC specification.
- Original Sender: The original sender of the email is the most likely recipient of an OOO message from commonly used email platforms.
- Sender Awareness: The original sender is typically informed of the recipient's absence.
- Internal vs External replies: Some email platforms provide options for handling internal vs external email replies.
- Deviation From Standards: Be aware that the common practice in email platforms deviates from the recommendations outlined in the RFC.
Technical article
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.
4 May 2024 - RFC Editor
Technical article
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.
6 May 2025 - IONOS
