Email routing is the process of directing emails from the sender's mail server to the recipient's mail server. Issues with email routing can lead to undelivered or delayed messages. This knowledge base provides an extensive guide to common email routing problems, their causes, and solutions.

Table of Contents

1. MX Record Misconfiguration

   • Description: Occurs when the Mail Exchange (MX) records of a domain are improperly configured.

   • Causes: Incorrect DNS settings, outdated MX records.

   • Solution: Verify and update MX records with the correct mail server addresses.

2. SPF/DKIM/DMARC Authentication Failures

   • Description: Emails fail SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), or DMARC (Domain-based Message Authentication, Reporting, and Conformance) checks.

   • Causes: Misconfigured authentication settings, missing or incorrect DNS records.

   • Solution: Correct SPF, DKIM, and DMARC records, and ensure they align with sending servers.

3. Incorrect Mail Exchanger Priority

   • Description: Incorrect priority values in MX records leading to email misdirection.

   • Causes: Misconfigured DNS settings, incorrect MX record priorities.

   • Solution: Verify and adjust MX record priorities to ensure correct mail routing.

4. Blacklisting of IP or Domain

   • Description: Emails are not delivered due to the sender's IP or domain being listed on a blacklist.

   • Causes: Sending spam, compromised accounts, poor email practices.

   • Solution: Remediate the issues leading to blacklisting, request delisting from relevant authorities.

5. Mail Server Downtime

   • Description: Mail servers are temporarily unavailable, leading to email delivery failures.

   • Causes: Maintenance, hardware failure, network issues.

   • Solution: Monitor server status, schedule maintenance during low traffic periods, and implement failovers.

6. Routing Loops

   • Description: Emails get caught in a loop and are repeatedly sent between servers.

   • Causes: Misconfigured forwarding rules, incorrect DNS settings.

   • Solution: Review and correct forwarding configurations, ensure DNS records are accurate.

7. Over-Quota Mailboxes

   • Description: Mailboxes are full, preventing the delivery of new emails.

   • Causes: Neglecting to manage mailbox sizes, inadequate storage allocation.

   • Solution: Monitor mailbox sizes, implement quotas, and provide users with instructions on managing their inboxes.

8. Misconfigured Email Clients

   • Description: Email clients are not set up to communicate with the correct mail servers.

   • Causes: Incorrect server settings, outdated client software.

   • Solution: Review and update email client configurations with the correct server details.

9. Greylisting

   • Description: Emails are temporarily rejected as a spam prevention measure.

   • Causes: Misconfiguration of greylisting settings, false positives.

   • Solution: Adjust greylisting parameters or whitelist trusted senders.

10. ISP or Firewall Blocking

    • Description: Emails are blocked by an Internet Service Provider (ISP) or a firewall.

    • Causes: Strict security settings, spam filtering.

    • Solution: Contact the ISP or firewall administrator to review and adjust blocking rules.

11. Incorrect DNS Settings

    • Description: DNS records, including MX, A, and CNAME records, are not properly configured.

    • Causes: Incorrect DNS entries, propagation delays.

    • Solution: Validate and update DNS records as needed, allow time for propagation.

12. Improper Routing Tables

    • Description: Network routing tables are not set up correctly.

    • Causes: Misconfigured routing rules, network changes.

    • Solution: Review and update routing tables to ensure proper email delivery paths.

Conclusion

Email routing problems can be complex and may arise from various sources. Understanding the common issues and their solutions is essential for maintaining reliable email communication. Regular monitoring, proper configuration, and timely updates are crucial steps towards resolving and preventing routing problems. Always keep documentation of your email infrastructure for reference in troubleshooting situations.