Summary
The X-Microsoft-Antispam-Mailbox-Delivery header is a crucial diagnostic element in Microsoft 365 and Exchange environments, offering detailed insights into the ultimate destination and handling of an email. While many of its values are primarily for Microsoft's internal use, specific indicators provide valuable information for senders and administrators. Key values confirm whether a message reached the inbox, junk folder, or was rejected, and can also reveal delivery to special mailboxes like those configured for out-of-office replies, journaling, or shared access. This header is indispensable for troubleshooting delivery issues, understanding the impact of mail flow rules, and verifying the final disposition of an email.
Key findings
- Delivery Destination Indicator: The X-Microsoft-Antispam-Mailbox-Delivery header indicates an email's final delivery destination within Microsoft 365 or Exchange, providing a clear signal about where the message landed.
- Common Value Meanings: Specific values reveal distinct delivery outcomes: 'dest:J' or 'Junked' confirms an email landed in the junk folder; 'dw:msft_user' signifies successful delivery to a standard Microsoft 365 user's mailbox; 'dw:oof' indicates delivery to a mailbox with an Out-of-Office reply configured.
- Special Mailbox Delivery: Values like 'dw:onof' (On-premises Non-Original Recipient) or 'dw:inof' (In-office Non-Original Recipient) denote delivery to non-primary mailboxes, such as journaling, shared, or compliance mailboxes, which are crucial for retention or specific routing scenarios.
- Final Disposition Status: This header provides clear final disposition statuses like 'Delivered' for inbox arrival, 'NotDelivered' or 'Blocked' for message rejection, and 'FilteredAsSpam' for messages that were delivered but flagged as spam, offering direct insights into the success or failure of delivery.
Key considerations
- Internal Focus: Many values within the X-Microsoft-Antispam-Mailbox-Delivery header are primarily intended for Microsoft's internal diagnostic purposes, which means they might not always be easily decipherable by external users without specific documentation.
- Troubleshooting Aid: For IT professionals and email administrators, this header is invaluable for troubleshooting email delivery issues in Microsoft 365. Analyzing its values helps determine the exact disposition of a message, whether it was delivered, redirected, or handled by a specific rule.
- Mail Flow Rule Impact: Mail flow rules, also known as transport rules, significantly influence the values present in this header. These rules dictate how messages are processed and routed, directly affecting the final mailbox delivery status.
- Tools for Analysis: Interpreting this header effectively often requires tools like the Message Header Analyzer, which helps to parse and provide insights into how a message was routed and ultimately delivered within Exchange Online, revealing the final mailbox destination type.
What email marketers say
8 marketer opinions
Expanding on its role as a diagnostic tool, the X-Microsoft-Antispam-Mailbox-Delivery header's specific values are critical for a granular understanding of how emails are processed and delivered within Microsoft 365 environments. This header is not merely about whether an email arrived, but precisely where it landed, whether it was an original recipient, or if special rules and mailbox configurations influenced its final disposition. For administrators and IT professionals, interpreting these values is essential for pinpointing delivery issues, verifying compliance, and understanding complex mail flow scenarios.
Key opinions
- Junk Folder Confirmation: The 'dest:J' value within the header explicitly confirms that an email arrived in the recipient's junk folder, providing a clear indication of its spam classification.
- Standard User Delivery: The 'dw:msft_user' value indicates successful delivery to a standard Microsoft 365 user's mailbox, confirming the message reached an active user account within the Microsoft ecosystem.
- Non-Primary Recipient Handling: Values like 'dw:onof' (On-premises Non-Original Recipient) and 'dw:inof' (In-office Non-Original Recipient) signify delivery to non-primary mailboxes, such as those used for journaling, compliance, or shared mailbox scenarios, distinguishing between on-premises and in-office environments.
- Out-of-Office Delivery: The 'dw:oof' value specifically indicates that the message was delivered to a mailbox configured to send an Out-of-Office (OOF) reply, signaling the recipient's current availability status.
Key considerations
- Troubleshooting Imperative: For IT professionals, analyzing the X-Microsoft-Antispam-Mailbox-Delivery header is crucial for troubleshooting email delivery issues within Microsoft 365 environments.
- Understanding Final Path: The header's values are instrumental in understanding the final delivery path and specific destination within Microsoft 365, which is vital for resolving routing issues or verifying recipient mailbox status.
- Internal Processing Insights: This header provides key internal information about how a message was ultimately processed and delivered, including details about redirects to shared mailboxes or distribution lists.
- Limited External Readability: It's important to note that certain parts of the X-Microsoft-Antispam-Mailbox-Delivery header are generally not readable or understandable by external users, as they are primarily for Microsoft's internal diagnostics.
Marketer view
Email marketer from Email Geeks explains that the 'dest:J' value within the X-Microsoft-Antispam-Mailbox-Delivery header confirms an email arrived in the junk folder, noting that other parts of the header are generally not readable by external users.
31 Jul 2024 - Email Geeks
Marketer view
Email marketer from Spiceworks Community shares that 'dw:onof' in the X-Microsoft-Antispam-Mailbox-Delivery header typically means 'On-premises Non-Original Recipient,' indicating delivery to an on-premises mailbox that wasn't the primary recipient, often seen in journaling or shared mailbox scenarios, distinguishing it from 'dw:inof' which refers to in-office non-original recipients.
27 Nov 2023 - Spiceworks Community
What the experts say
3 expert opinions
The X-Microsoft-Antispam-Mailbox-Delivery header is instrumental for understanding the definitive outcome of an email's journey within Microsoft environments. It serves as a direct indicator of whether a message reached the recipient's inbox, was routed to the junk folder, or faced rejection. While parts of this header are designed for Microsoft's internal diagnostic use, key values provide clear, actionable insights for email senders and administrators regarding final delivery status.
Key opinions
- Final Delivery Outcome: This header explicitly indicates the ultimate delivery decision for an email within the recipient's mailbox, providing clarity on its final destination.
- Specific Status Meanings: Values like 'Delivered' denote inbox placement, 'NotDelivered' or 'Blocked' signify rejection, and 'Junked' means the message went to the junk folder, offering a granular view of message disposition.
- Spam Filtering Insights: The 'FilteredAsSpam' value reveals that a message was delivered but simultaneously flagged as spam, indicating an important classification by Microsoft's systems.
- Primary Diagnostic Purpose: Although some information is publicly discernible, many values within the header are primarily designed for Microsoft's internal diagnostic and troubleshooting purposes.
Key considerations
- Troubleshooting Deliverability: Email senders can use this header to diagnose why messages might not be reaching the intended inbox, specifically to identify rejections or junk folder placement.
- Monitoring Delivery Statuses: Regularly checking this header's values helps email marketers and administrators monitor their deliverability performance, especially regarding inbox placement versus junking or blocking.
- Anticipated Value Expansion: As Microsoft continues to refine its email systems, senders should expect and be prepared for the introduction of additional values to this header, offering more detailed delivery insights over time.
- Complementary Analysis: For a comprehensive understanding of email flow, it is beneficial to analyze the X-Microsoft-Antispam-Mailbox-Delivery header in conjunction with other diagnostic headers.
Expert view
Expert from Email Geeks explains that the values in the X-Microsoft-Antispam-Mailbox-Delivery header are primarily for Microsoft's internal diagnostic purposes.
6 Dec 2022 - Email Geeks
Expert view
Expert from Spam Resource explains that the X-Microsoft-Antispam-Mailbox-Delivery header is a new Microsoft header indicating the final delivery decision for the mailbox. He notes that values like 'NotDelivered' mean the message was rejected, while 'Delivered' means it reached the inbox. He anticipates more values will be added over time.
1 Oct 2024 - Spam Resource
What the documentation says
3 technical articles
The X-Microsoft-Antispam-Mailbox-Delivery header provides granular detail about an email's ultimate path and handling within Microsoft 365. It clarifies the final destination, offering specific values that indicate whether a message reached a standard user, triggered an out-of-office reply, or was directed to a non-delivery list. The presence and interpretation of these header values are significantly shaped by an organization's mail flow rules, and tools like the Message Header Analyzer are essential for deciphering this crucial data for effective email diagnostics and understanding routing.
Key findings
- Specific Delivery Outcomes: The X-Microsoft-Antispam-Mailbox-Delivery header explicitly indicates the email's precise delivery outcome within Microsoft 365, showcasing if it reached a standard user, an out-of-office responder, or a non-delivery list.
- Influenced by Mail Flow Rules: Mail flow rules, also known as transport rules, significantly determine the values present in this header, dictating how messages are processed and affecting the final mailbox delivery status.
- Role of Diagnostic Tools: Tools such as the Message Header Analyzer are indispensable for accurately interpreting the X-Microsoft-Antispam-Mailbox-Delivery header, aiding in diagnosing routing and delivery within Exchange Online.
Key considerations
- Understanding Delivery Paths: Deciphering the values in this header, such as 'dw:msft_user' or 'dw:oof', is crucial for understanding the specific delivery path and final disposition of an email within Microsoft 365.
- Impact of Internal Rules: Administrators must recognize that custom mail flow rules can alter expected header values, leading to specific outcomes like 'nondl' or 'msft_dl' based on rule actions.
- Utilizing Analyzer Tools: Employing the Message Header Analyzer tool is highly recommended for effectively parsing and gaining insights from this header, which is vital for troubleshooting and verifying email flow in Exchange Online.
Technical article
Documentation from Microsoft Learn explains that the X-Microsoft-Antispam-Mailbox-Delivery header indicates the message's delivery destination within Microsoft 365, with common values such as 'dw:msft_user' for a standard Microsoft 365 user, 'dw:oof' for an out-of-office reply, and 'dw:nondl' for a non-delivery list, providing specific insights into how the email was finally handled.
13 Aug 2021 - Microsoft Learn
Technical article
Documentation from Microsoft Learn explains that mail flow rules (transport rules) can influence the values seen in the X-Microsoft-Antispam-Mailbox-Delivery header, as these rules determine how messages are processed and routed, potentially leading to values like 'nondl' (non-delivery list) or 'msft_dl' (Microsoft distribution list) depending on the rule's action, thereby affecting the final mailbox delivery status.
13 Nov 2021 - Microsoft Learn
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