What do web.de bounce codes like c=hd and c=hi mean?

Key findings

• Header issues: The c=hd code specifically indicates an issue with the Date: header's formatting, which web.de may deem non-compliant. This highlights web.de's strict adherence to header standards, as outlined in RFCs (such as RFC 5322).
• Undocumented codes: The meaning of c=hi remains largely unknown and is not explicitly documented by web.de, though it is suspected to relate to other header integrity or content issues.
• Blacklist/blocklist indication: c=sp often signifies that the sending domain or IP is listed on a blacklist (or blocklist), potentially Spamhaus, impacting deliverability. For more information on blacklists, see our in-depth guide to email blocklists.
• Rate limiting: c=irlrm indicates that emails are being sent too quickly, triggering web.de's rate limiting policies.
• ISP specificities: Web.de's policies, especially concerning header formats, can be more particular than those of other major email providers.

Key considerations

• Vague error messages: The generic 554 Reject due to policy restrictions message is not actionable on its own, necessitating deeper investigation into the appended codes.
• Postmaster page limitations: While web.de provides a postmaster page, it often lacks the granular detail needed to interpret these highly specific sub-codes.
• Systematic testing: To identify the root cause of rejections, a systematic approach to testing different email headers and content elements is often required. Understanding how email service providers classify and manage bounce codes is essential.
• Proactive outreach: In cases where documentation and support are insufficient, reaching out to senior contacts within the ISP or leveraging community knowledge may be necessary.

Key opinions

• Limited granularity: While web.de's postmaster site provides some general information, it doesn't offer the granular detail required to understand specific proprietary codes. Understanding email bounce error codes is crucial.
• Vague generic messages: Generic error messages, such as 554 Reject due to policy restrictions, are perceived as unhelpful due to their lack of specific actionable information.
• Necessity for self-deciphering: Marketers frequently find themselves needing to decode web.de's URL parameters or specific codes independently, suggesting a gap in official documentation.
• Strict compliance: Web.de's policies, such as the specific requirement for the Date: header (causing c=hd bounces), can be more stringent than those of other major email providers.

Key considerations

• Beyond support: Many marketers find that standard support channels or postmaster pages yield generic, unhelpful responses, pushing them to seek alternative solutions like direct outreach or community forums.
• Importance of hidden codes: When a bounce URL contains a specific, proprietary code, it indicates a distinct underlying issue that, while not publicly explained, can often be resolved through methodical testing and understanding the various policy-related bounce messages.
• Systematic testing: When facing undocumented errors, systematically experimenting with different content elements, headers, and sending patterns is essential to pinpoint the cause of the rejection.
• Holistic deliverability strategy: Addressing these specific web.de issues is part of a broader strategy to improve overall email deliverability.

Key opinions

• Lack of clarity: Generic bounce messages such as 554 Reject due to policy restrictions are considered unhelpful because they do not specify whether the issue is technical, policy-based, or recipient-related. This makes it hard for email service providers to classify and manage SMTP bounce codes.
• Inadequate postmaster pages: While web.de provides a postmaster page, experts argue its explanations are insufficient when senders need to understand specific, undocumented codes like c=hi.
• Need for precise differentiation: Experts believe that helpful bounce messages would clearly differentiate between header-based, domain-based, and IP-based rejections, rather than lumping them under a single broad policy violation.
• Burden on senders: The current system often forces senders to engage in aimless speculation or extensive self-investigation to decode specific URL parameters and understand the precise reason for rejection.
• Conflation of issues: Combining distinct issues, such as a syntax error in email headers (see what RFC 5322 says vs. what actually works) and excessive spam complaints, into a single generic message is considered unhelpful for effective remediation.

Key considerations

• Full diagnostic data: Proper diagnosis of bounce issues, especially with elusive codes, often requires access to the complete SMTP transaction log and the headers of the rejected email.
• ISP transparency: While web.de provides some information, experts suggest that ISPs, in general, could be more transparent with their proprietary bounce codes to assist senders.
• Proactive best practices: Adhering to strict email best practices and anticipating potential issues with highly particular ISPs can mitigate many deliverability challenges. For more, see the insights on technical solutions from top performing senders.
• Community insight: Given the lack of official documentation for certain codes, community discussions (like on SpamResource.com) become crucial for deciphering and sharing solutions.

Key findings

• Bounce code basics: General documentation defines email bounce codes as numeric messages indicating why an email could not be delivered to the recipient, categorizing them into various types of email bounces.
• SMTP 5xx errors: The 554 code, a common SMTP permanent rejection, signifies a failure in the transaction (e.g., due to policy restrictions), meaning no further attempts will be made to deliver the email.
• RFC compliance: RFCs (Request For Comments) like RFC 5321 and RFC 5322 define the technical specifications for email, and strict adherence to these, especially for email headers, is often expected by ISPs like web.de.
• Proprietary codes: Specific, proprietary sub-codes such as c=hd or c=hi are typically not detailed in general documentation, requiring senders to infer their meaning.

Key considerations

• Bounce type understanding: Distinguishing between soft and hard bounces is crucial for managing email lists and determining if reattempts are advisable.
• Full bounce message analysis: Even with generic SMTP codes, the full bounce message, including any appended proprietary codes or URLs, provides critical clues for troubleshooting.
• Sender compliance: Compliance with general email best practices and RFC standards helps minimize rejections, as many policy restrictions are rooted in these fundamental guidelines.
• Inference and adaptation: When explicit documentation for proprietary codes is unavailable, senders must infer meanings based on patterns of rejections and adapt their sending practices accordingly.