What problems can redundant email forwarding cause and how to fix it?

Key findings

• Authentication issues: Redundant forwards can break authentication protocols like SPF, DKIM, and DMARC, leading to messages being flagged as suspicious or spam. This is a common issue, as the forwarding server may alter the message in a way that invalidates the original authentication signatures. Learn more about how email forwarding affects DMARC policies.
• Duplicate emails: A common consequence of improper forwarding is the delivery of multiple copies of the same email to recipients, leading to frustration and potential confusion, especially in customer service environments.
• Email loops: A mailbox forwarding to itself can create an infinite loop, causing a flood of duplicate messages and potentially overloading mail servers. This can result in service disruptions and may even lead to your domain or IP being placed on a blacklist (or blocklist).
• Spam and blocklisting risks: Forwarding spam or malicious content can increase the likelihood of your domain being blocklisted by receiving mail servers due to the perceived poor quality of traffic originating from your forwarding setup. This directly impacts your email domain reputation.
• Undetected dependencies: Sometimes, redundant forwards are remnants of old configurations or integrations with third-party applications. Removing them without proper investigation can inadvertently break critical workflows or disrupt essential services.

Key considerations

• Review existing forwards: Before making any changes, thoroughly audit all email forwarding rules associated with affected mailboxes. Identify any self-referencing forwards or unusual multiple forwarding paths.
• Check application dependencies: Investigate if any external applications or internal systems rely on specific forwarding configurations. Consult with IT teams or application administrators to understand potential impacts of changes.
• Test changes cautiously: Implement changes incrementally and test thoroughly after each modification. Send test emails to the affected addresses and monitor delivery to ensure expected behavior. This is part of any good email deliverability strategy.
• Monitor deliverability: After resolving redundant forwards, continue to monitor email deliverability metrics, including bounce rates, spam complaints, and inbox placement, to ensure long-term stability.
• Prioritize proper authentication: Ensure your domain's SPF, DKIM, and DMARC records are correctly configured and remain valid even after forwarding changes to maintain optimal sender reputation and avoid spoofing issues.

Key opinions

• Unexpected self-forwarding: Marketers have observed scenarios where a mailbox forwards to itself alongside other intended destinations, leading to confusion and potential issues.
• Impact on ticketing systems: Redundant forwards can cause customer service ticketing systems to create duplicate tickets for a single incoming email, complicating issue tracking and response times.
• Migration-related issues: Email migrations often introduce unforeseen forwarding problems, including persistent duplicate emails that are difficult to resolve without recreating mailboxes.
• Attachment delivery failures: Some users report issues with attachments failing to send or being corrupted when emails are forwarded, hindering effective communication.
• Undiscovered application dependencies: Forwarding rules that seem redundant might actually be crucial for older or less visible applications, making their removal risky without thorough investigation. This is often the cause of email deliverability issues.

Key considerations

• Identify forwarding intent: Confirm the purpose of each forwarding rule to avoid inadvertently disrupting email flow or critical system integrations.
• Test modifications: Any changes to forwarding settings should be tested rigorously with various email types (plain text, HTML, attachments) to verify correct delivery and formatting. Ensure you are not generating a bounce after opening.
• Monitor ticketing systems: If forwarding impacts service desks, closely monitor ticket creation to detect and address duplication issues promptly.
• Address underlying causes: For persistent duplication or forwarding failures, investigate mail server configurations and potential loops. Digital Creatings highlights the importance of removing email forwarding loops to prevent errors.

Key opinions

• Authentication breakdown: Experts warn that email authentication can easily break when messages are forwarded, especially if the forwarding mechanism modifies the message headers or body in a way that invalidates SPF or DKIM signatures. For instance, DMARC policies are particularly sensitive to forwarding.
• Spam propagation risks: Forwarding, especially redundant or open forwarding, can unintentionally propagate spam or malicious content, increasing the risk of the sending domain or IP being added to email blacklists.
• MTA rule variations: Different Mail Transfer Agent (MTA) rules and filters on receiving domains mean that the impact of forwarding, particularly with spam-like content, can vary significantly, making troubleshooting complex.
• Looping issues: Self-referencing forwards or circular paths can create endless email loops, consuming server resources and potentially leading to service disruption or blacklisting due to excessive mail volume. This can also cause external forwarding errors.
• Increased attack surface: Redundant forwarding can inadvertently expand the attack surface for spoofing and phishing attempts if not properly secured, as it adds more points of potential compromise.

Key considerations

• Implement DMARC carefully: When using DMARC, be aware that forwarding can cause legitimate emails to fail DMARC checks. Consider a policy of p=none initially to gather data before enforcing stricter policies.
• Monitor for loops: Regularly check mail logs and server performance for signs of email loops caused by redundant forwarding configurations. This is critical for maintaining server health.
• Educate on forwarding best practices: Advise users against creating informal forwarding chains, particularly to external addresses, as these can easily lead to deliverability issues.
• Leverage DMARC reporting: Utilize DMARC aggregate reports to identify legitimate forwarded emails that are failing authentication, providing insights into potential issues with specific forwarding paths. Spamresource.com provides extensive resources on DMARC and its complexities.

Key findings

• Mail server behavior: Mail server configurations dictate how forwarding rules are processed, and incorrect settings can lead to unintended self-referencing or circular paths, resulting in mail loops.
• Bounce message diagnostics: Bounce-back error messages are critical for diagnosing email forwarding failures, providing specific codes or descriptions that indicate the root cause, such as loops or authentication failures.
• Spam filter interaction: Receiving mail servers' spam filters can flag forwarded messages as suspicious, directing them to spam folders or blocking them entirely, especially if authentication is broken or content seems anomalous.
• Header alterations: Forwarding often involves rewriting mail headers, which can disrupt SPF and DKIM validation. This is a primary reason why forwarded emails often face DMARC failures and can affect overall email deliverability.
• Format integrity: Email clients and forwarding services may handle formatting differently, leading to disruptions, duplicated elements, or altered layouts in forwarded messages.

Key considerations

• Understand RFC compliance: Adhere to RFC standards for email forwarding to minimize deliverability issues. Knowing what RFC 5322 says versus what actually works is key.
• Configure loop prevention: Ensure your mail server is configured with appropriate loop detection and prevention mechanisms to avoid endless forwarding cycles and server overloads.
• Monitor spam folders: Regularly check spam or junk folders on destination accounts when troubleshooting forwarded emails, as legitimate messages may be misclassified.
• Review SMTP settings: Examine SMTP configurations for any settings that might inadvertently cause duplicate sent copies or other forwarding anomalies. Zoho Mail's documentation provides useful insights into SMTP server settings.