Summary
The Vade Secure OXSUS0001_403 error code, often accompanied by a 550 5.7.1 Connection refused SMTP response, presents a significant challenge for email senders due to its ambiguous nature. This single error code is used by Vade Secure to convey two distinct reasons for non-delivery. One interpretation indicates that the message was sent to a non-existent customer or user, which for bulk mailers, means the recipient should be unsubscribed. The other interpretation points to an invalid format of the recipient's address in the RCPT TO command, impacting all mail types. This dual meaning complicates automated bounce processing and accurate list management, making it difficult for senders to determine the exact cause and appropriate remedial action for each bounce.
Key findings
- Dual interpretation: The OXSUS0001_403 error can mean either a non-existent user (for bulk mail) or an invalid recipient address format (for all mail).
- SMTP response: This Vade Secure specific code is typically paired with the generic SMTP error 550 5.7.1 Connection refused.
- Action for bulk mailers: If you are a bulk mailer and receive this error, Vade Secure's guidance is to treat it as an unsubscribe or a hard bounce.
- Inconsistent reporting: The same recipient might sometimes receive mail and other times trigger this error within a short period, leading to confusion.
Key considerations
- Bounce handling: Given the ambiguity, it is safest to treat OXSUS0001_403 as a permanent failure for bulk mail, meaning the address should be removed from your list to maintain good email deliverability. For more on how 4xx mail errors should be handled, refer to our dedicated guide.
- Recipient list hygiene: Despite the error's dual nature, consistent list cleaning for non-existent users remains crucial.
- Error code interpretation: Understanding how to interpret SMTP error codes, including those specific to providers like Vade Secure, is vital for troubleshooting. Learn more about how to find and interpret SMTP error codes.
- Consult Vade Secure documentation: For the most authoritative information, always refer to the Vade Secure postmaster site for their latest error response definitions.
What email marketers say
Email marketers grappling with the Vade Secure OXSUS0001_403 error code express frustration over its lack of clarity. The core issue for many is that the same error code is used for different scenarios, making it challenging to automate bounce handling processes effectively. They report observing both successful deliveries and immediate rejections (403 errors) for the exact same recipient within short timeframes, which further complicates efforts to maintain accurate contact lists and prevent impacts to sender reputation.
Key opinions
- Conflicting definitions: Marketers find it perplexing that Vade Secure provides two distinct definitions for the identical OXSUS0001_403 error, depending on whether the mail is considered bulk or transactional.
- Inconsistent behavior: There are reports of the error code appearing for recipients who are known to be active, and even alongside successful deliveries to the same address within minutes.
- Classification confusion: The internal classification by Vade Secure of an email as bulk versus non-bulk for applying the error code is not always clear to senders.
Key considerations
- Impact on segmentation: Ambiguous errors hinder a marketer's ability to accurately segment and clean their email lists based on true deliverability issues versus transient problems or misclassifications.
- List hygiene best practices: Despite the confusion, maintaining rigorous list hygiene is paramount to avoiding blocks and improving overall inbox placement. Regularly auditing your mailing list helps, especially regarding potentially invalid recipients. Consider our guide on why emails go to spam.
- Seeking clarification: Marketers are actively trying to engage Vade Secure for clearer definitions or distinct error codes to better manage bounces.
- Monitor blocklists: Although this is an error code, not a blocklist entry, consistent high bounce rates can lead to blacklisting. Monitoring various blocklists is crucial for staying ahead of potential deliverability issues. Read our in-depth guide to email blocklists for more information.
Marketer view
A marketer from Email Geeks indicates that they are encountering OXSUS0001_403 errors, which suggest a non-existent user, despite the user being active. This discrepancy highlights a major challenge in accurately identifying invalid recipients.
Marketer view
A marketer from Email Geeks states that there appear to be two different definitions for the OXSUS0001_403 error code in Vade Secure's documentation. One implies a non-existent user for bulk mailers, advising an unsubscribe, while the other suggests an invalid recipient address format.
What the experts say
Deliverability experts underscore the critical need for distinct and clear bounce codes to ensure efficient and accurate email delivery. An ambiguous error like Vade Secure's OXSUS0001_403, which covers both non-existent users and format issues, can lead to misinterpretations and poor list hygiene practices. Experts advise that while senders should always strive for pristine data, mail servers should provide actionable feedback. They also emphasize the importance of robust email authentication (SPF, DKIM, DMARC) to build trust, which can sometimes influence how ambiguous errors are treated by recipient systems.
Key opinions
- Clarity is key: Ambiguous error codes hinder a sender's ability to precisely identify and fix underlying issues, impacting overall deliverability rates.
- Impact on reputation: Misinterpreting bounces can lead to continued sending to problematic addresses, which negatively affects sender reputation and can result in blocklistings.
- Technical standards: While SMTP standards allow for general error messages, the trend in deliverability is towards more granular feedback for better sender control.
Key considerations
- Proactive hygiene: Even with ambiguous errors, a strong focus on maintaining a clean email list is the best defense against deliverability issues. This includes regularly removing invalid or unengaged contacts.
- Authentication protocols: Ensure your domain's SPF, DKIM, and DMARC records are correctly configured. Strong authentication builds trust and can sometimes help mitigate blocks, even in the face of unclear bounce responses. Review our guide on DMARC, SPF, and DKIM.
- Domain reputation monitoring: Continuously monitor your domain's reputation to identify trends that might indicate problems, even if specific error codes are unhelpful. A practical guide to understanding your email domain reputation is available.
- Engage with ISPs: For persistent issues, directly contacting the postmaster or abuse desk of the affected ISP (like Vade Secure) can sometimes yield more specific insights, even if general error pages are vague. Further information on what to do when your email is blocked can be found.
Expert view
An expert from SpamResource highlights that for deliverability, clear error codes are paramount. When a single code denotes multiple issues, it creates an unnecessary burden on senders to correctly interpret and react, often leading to over-suppression or persistent sending to invalid addresses.
Expert view
An expert from Wordtothewise notes that ISPs should prioritize providing actionable bounce messages. Ambiguous errors, such as those that combine non-existent user with invalid format, undermine automated feedback loops that are essential for large-scale email operations.
What the documentation says
Vade Secure's own documentation for the OXSUS0001_403 error code explicitly states two interpretations, which adds to the complexity for senders. The primary definition, often paired with 550 5.7.1 Connection refused, suggests that the email was sent to a non-existent customer or user. For bulk mailers, this is a clear instruction to unsubscribe the recipient. The secondary definition indicates an invalid format of the recipient's address in the RCPT TO command. This dual usage of a single error code, particularly a 550 class (permanent failure) code, poses a challenge for automated systems trying to accurately distinguish between a permanent invalidation and a transient format issue.
Key findings
- Primary reason: The message was sent to a non-existent customer or user. If the sender is a bulk mailer, this should result in an unsubscribe.
- Secondary reason: The format of the recipient's address provided in the RCPT TO command is invalid.
- SMTP code: The error is presented with an SMTP 550 5.7.1 Connection refused status.
Key considerations
- RFC compliance: While SMTP 5xx codes generally mean permanent failure, the specific internal codes (like OXSUS0001_403) and their varied interpretations can diverge from RFC intent for clear diagnostics. Understand what RFC 5322 says versus what actually works.
- Sender responsibility: Documentation places the onus on the sender to interpret the error based on their mail type and take appropriate action, such as unsubscribing for bulk mail.
- Authentication impact: The documentation mentions checking SPF, DMARC, and MAIL FROM sender as general advice. Ensuring these are robust can help with overall deliverability. See a list of DMARC tags and their meanings.
- Postmaster engagement: The documentation itself is found on the Vade Secure postmaster site, indicating it's the primary resource for sender questions.
Technical article
Vade Secure documentation defines OXSUS0001_403 with the accompanying 550 5.7.1 SMTP response as indicating that the message was sent to a non-existent customer or user. It explicitly states that bulk mailers should treat such errors as an unsubscribe.
Technical article
Vade Secure documentation also states that the OXSUS0001_403 error, combined with a 550 5.7.1 Connection refused, signifies that the format of the recipient's address provided in the RCPT TO command was invalid. This second definition adds complexity to automated bounce processing.
Related pages
How to find and interpret SMTP error codes?
How should 4xx mail errors be handled and when should they be considered bounces?
A simple guide to DMARC, SPF, and DKIM
An in-depth guide to email blocklists
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
What RFC 5322 Says vs. What Actually Works
A practical guide to understanding your email domain reputation
List of DMARC tags and their meanings
What does the "error dialing remote address" bounce code mean and is it controllable?
What causes '550 relaying denied' bounce errors and how to resolve them?
