Why are T-online.de and Arcor.de hard bouncing with local policy and permission errors?

Key findings

• Sudden increase: A client experienced a drastic rise in hard bounces from T-online.de and Arcor.de, from dozens to thousands, within two weeks, despite years of smooth delivery.
• Specific error codes: The primary bounce messages were (5.7.0) Local Policy Violation and (5.7.1) Permissions problem, alongside generic 'Unspecified error during delivery'.
• Sender reputation or blocklisting: These errors strongly suggest that the sender's IP or domain has been blocklisted, either globally or specifically by T-online/Arcor.de, or that there's a policy violation.
• Authentication requirements: German ISPs, including T-online, are known for strict authentication and compliance requirements, such as proper rDNS setup, which must be followed.

Key considerations

• Direct postmaster contact: The most effective way to resolve specific ISP blocks is often to contact their postmaster team directly. Look for contact forms or dedicated postmaster pages, such as the one for T-online.de.
• Review list acquisition: Even with double opt-in, ensure no open forms or vulnerabilities allow spammers to introduce bad addresses. This helps avoid issues that contribute to hard bounces from various domains.
• Check sender reputation: Verify your domain and IP addresses have a good reputation. Tools that monitor sender reputation can provide insights into potential issues.
• Monitor for invalid addresses: The 'permissions problem' can sometimes indicate sending to an invalid or non-existent address, which might appear similar to domain does not exist errors, necessitating aggressive list cleaning.

Key opinions

• Unforeseen blocks: Marketers frequently express surprise when email programs that have worked for years suddenly encounter significant hard bounce issues.
• Limited diagnostic tools: Despite using various testing methods, marketers often struggle to identify the precise reason behind a sudden surge in hard bounces.
• Reliance on established practices: Many trust their list acquisition methods, such as double opt-in and on-site checkboxes, to prevent deliverability problems.
• Need for resolution: The primary concern for marketers is finding actionable steps to get unblocked and restore normal email flow as quickly as possible.

Key considerations

• Proactive testing: Regularly perform email deliverability tests to catch potential issues before they escalate into widespread hard bounces.
• Understanding bounce types: Familiarize yourself with the differences between hard and soft bounces to prioritize fixes and manage your email list effectively. A good resource is why email bounces.
• Ongoing deliverability monitoring: Continuous monitoring of email deliverability rates is crucial, as deliverability issues can fluctuate and impact inbox placement without direct notification.
• Review subscriber acquisition: Even with strong opt-in processes, periodically audit your forms to ensure they are not vulnerable to automated attacks that could lead to invalid addresses being added.

Key opinions

• Block indication: A 'Local policy violation' error code almost always means the sender is blocklisted by the receiving server.
• List hygiene issues: A 'Permissions problem' often suggests the email is being sent to a mailing list that does not permit non-subscribers to send to it, potentially indicating bad addresses.
• ISP specific requirements: ISPs like T-online have strict requirements for authentication, including proper rDNS setup, and expect all sending rules to be followed diligently.
• IP range blocks: Some ISPs might block entire IP ranges, especially from certain data centers, which can inadvertently affect smaller legitimate senders.

Key considerations

• Direct communication: Engaging directly with the ISP's postmaster team, even if they are known for being challenging, is a critical step in resolving a block.
• Review acquisition sources: Rethink how email addresses are acquired if there is any chance of spammers injecting invalid addresses, as this can severely impact domain reputation.
• Understand blocklist mechanics: Educate yourself on how different types of email blocklists (or blacklists) operate, as a block can originate from various sources.
• Continuous monitoring: Implement robust monitoring of bounce rates and deliverability issues to identify and address problems swiftly. More information is available on why email bounces.

Key findings

• Permanent failure codes: SMTP 5.x.x error codes, like 5.7.0 and 5.7.1, denote permanent delivery failures, indicating that the message cannot be delivered as currently configured.
• Policy enforcement: 'Local policy violation' means the receiving server's internal rules prevented delivery, often related to sender reputation, authentication, or content.
• Authorization issues: 'Permissions problem' (5.7.1) suggests the sender lacks authorization to send to the specific recipient or mailing list, or the address is a spam trap.
• Unspecified errors: These generic errors often mask underlying policy or permission issues that the server cannot explicitly define or chooses not to for security reasons.

Key considerations

• Adherence to standards: Ensure your email setup fully complies with SMTP standards, including proper RFC 5321, to minimize rejection risks.
• Authentication configuration: Properly configure SPF, DKIM, and DMARC to ensure your emails are authenticated and less likely to be flagged as policy violations.
• List hygiene protocols: Implement rigorous list cleaning processes to remove invalid or problematic email addresses that could trigger permission errors and protect your sender reputation.
• Regular reputation checks: Consistently monitor your IP and domain reputation to detect any signs of being added to internal or external blocklists that could lead to policy-based rejections.