How to troubleshoot email delivery issues related to RFC compliance errors?

Key findings

• Bounce messages: Error messages such as "554 Message not accepted due to failed RFC compliance" are direct indicators of non-adherence to email standards.
• Yahoo's strictness: Yahoo, along with other major ISPs, can be particularly strict about RFC compliance, rejecting emails that other, more lenient providers might accept.
• Common culprits: RFC compliance issues frequently stem from improperly formatted headers (e.g., Date, From fields), incorrect line lengths, or issues with character encoding (e.g., high ASCII without proper QP or Base64 encoding).
• Duplicate sender: A specific instance of an RFC compliance failure involved a client inadvertently duplicating their sender address within the friendly from field.
• API vs. SMTP: The rise of custom APIs and homegrown message injectors for sending email can introduce compliance issues if these systems do not validate messages against RFCs as thoroughly as traditional SMTP.

Key considerations

• Header inspection: The first step in troubleshooting should always be a meticulous examination of the email headers to identify any malformed or missing fields.
• DNS records: Ensure that DNSSEC, DKIM, SPF, and DMARC records are correctly configured and haven't been inadvertently broken by recent updates.
• Protocol adherence: Verify correct termination of lines with CR/LF, proper MIME types, and accurate negotiation of TLS.
• Content and links: Check for bare IP addresses in links and ensure message line lengths comply with RFC standards.
• Postmaster contact: For specific ISP rejections, contacting their postmaster team (e.g., postmaster@) can sometimes provide direct assistance or insights into the exact RFC violation.

Key opinions

• Client-side issues: Many RFC compliance problems originate from how clients or their sending platforms configure their email, such as inadvertently duplicating sender addresses in the friendly from field.
• ISP variations: Marketers note that some ISPs are more forgiving of RFC non-compliance than others, meaning a message that delivers to one provider might be rejected elsewhere without any changes to the sender's configuration.
• Header visibility: Accessing and interpreting full email headers, especially from the receiving server, is often difficult but essential for identifying the precise RFC violation.
• Special characters: The presence of special characters in fields like the friendly from can trigger RFC non-compliance rejections, particularly with sensitive receiving systems like Yahoo's.
• Learning curve: RFC compliance issues can be complex and infrequent, presenting a steep learning curve even for experienced marketers when they arise.

Key considerations

• Proactive monitoring: Implementing internal monitoring for email formatting and header compliance can prevent critical delivery issues before they occur.
• Bounce message analysis: Even generic bounce messages like "554 RFC compliance" require thorough investigation, as the exact meaning can vary depending on the context and receiving ISP.
• Communication with recipients: While challenging, obtaining bounced email headers or test messages from the receiving side is invaluable for diagnosis.
• Platform-specific nuances: Be aware that certain platforms or configurations (e.g., using Outlook headers for Yahoo bounces) may not provide the direct insights needed for troubleshooting, necessitating alternative approaches.
• Understanding RFC 5322: A deeper understanding of email format compliance as outlined in RFC 5322 is critical for avoiding formatting-related rejections.

Key opinions

• Yahoo's pickiness: Deliverability experts agree that Yahoo is notably stricter about RFC compliance, often rejecting emails that other providers might accept, indicating a technically problematic email.
• DNS importance: A Deliverability expert from Email Geeks recommends checking DNS configuration, including DNSSec, SPF, DKIM, and DMARC, as a broken DNS update can lead to RFC compliance failures.
• Header and formatting: Common RFC violations include incorrect line lengths, improper CR/LF termination, bare IP addresses in links, and issues with MIME types or high ASCII character encoding without proper conversion.
• Date header errors: Incorrectly formatted or missing Date headers can flag emails as 'Invalid SMTP' by some systems, even if accepted.
• Sender responsibility: When a bounce message indicates an RFC violation, the sender is responsible for troubleshooting their own system, not the receiving ISP.
• API challenges: The increasing use of APIs and homegrown message injectors for sending mail, rather than traditional SMTP, is expected to lead to more RFC compliance issues if these tools do not adequately check for compliance.

Key considerations

• Reference RFC documents: RFC 5321 and RFC 5322 are the canonical references for understanding email protocol and message format compliance, respectively, and should be consulted directly.
• Comprehensive checks: Always verify TLS negotiation, MIME types, character encoding, and the correct formation of all email headers.
• Pre-send validation: Implement robust validation within custom sending platforms or APIs to ensure RFC compliance before messages are sent, preventing rejections down the line.
• Escalation procedures: While self-troubleshooting is key, engaging with the receiving ISP's postmaster team can provide targeted assistance for complex cases, but only after initial internal checks are exhausted.
• DMARC reports: Reviewing DMARC reports can sometimes indirectly point to underlying RFC issues if they impact authentication alignment.

Key findings

• RFC 5321: This document defines the core SMTP (Simple Mail Transfer Protocol), governing how email servers communicate and transfer messages, ensuring reliable and compliant mail delivery.
• RFC 5322: This RFC outlines the Internet Message Format, detailing the precise structure and content requirements for email messages, including all headers and the message body.
• RFC 3463: This document introduces enhanced mail system status codes, which provide more detailed diagnostic information in delivery status reports (DSRs), aiding in pinpointing specific RFC compliance failures.
• Common non-compliance: Misconfigurations such as incorrect date headers in email scripts are frequently cited as reasons for RFC non-compliance.
• Impact on delivery: Failing RFC 5322 compliance, especially regarding formatting, can result in hard bounce errors like "554 Message not allowed" from receiving servers.

Key considerations

• Authoritative sources: Always refer to the official IETF RFC documents (e.g., RFC 5321, RFC 5322) for precise definitions and requirements regarding email protocols and formats.
• Header and body structure: Pay close attention to the specified structure of email headers and body content, including character sets and line lengths.
• Error code interpretation: Utilize RFC 3463 and other error libraries to accurately interpret bounce messages and pinpoint the nature of the RFC non-compliance.
• Script updates: Regularly review and update mail sending scripts or applications to ensure they adhere to current RFC standards, especially concerning date formats and header fields.
• Holistic approach: Recognize that RFC compliance intertwines with other deliverability factors, such as DNS, SPF, DKIM, and DMARC settings, necessitating a comprehensive troubleshooting perspective.