What causes bounces from Barracuda-based domains and how to resolve them?

Key findings

• Barracuda blocks: Bounces with 550 permanent failure: blocked suggest the Barracuda gateway itself is rejecting the email, potentially due to sender reputation, content filtering, or authentication failures.
• User-implemented vs. system-wide: If only some recipients at Barracuda-protected domains are bouncing, it points to user-specific blocks (e.g., individual blacklists or content filters). If all emails to all addresses on all Barracuda domains are failing, it indicates a broader Barracuda system block affecting your sending IP or domain.
• Sender reputation: A common reason for blocks is poor sender reputation (domain or IP). Barracuda leverages Barracuda Central to identify known spammers, which can lead to blocks if your sender score is low. Understanding your domain reputation is essential.
• Content filtering: Barracuda provides extensive content filtering options. This means certain keywords, attachments, or message structures can trigger blocks, even if your sender reputation is good.

Key considerations

• Analyze bounce messages: The specific bounce message, especially the full text, often contains clues about why the email was rejected.
• Check Barracuda blocklists: Verify if your sending IP or domain is listed on Barracuda's internal blocklists. While public blocklists are important, private ones used by security gateways are equally critical. You can learn more about how to resolve Barracuda blocklist issues on our site.
• Review content and sender authentication: If the issue is user-implemented or content-related, adjust your email content to be less spammy and ensure your sender authentication (SPF, DKIM, DMARC) is properly configured.
• List hygiene: For consistent user-implemented blocks, removing those problematic addresses from your mailing list permanently is often the best long-term solution to avoid recurring bounces and protect your sender reputation.

Key opinions

• Sender frustration: Many marketers report experiencing Barracuda bounces even after checking their IPs and domains on common blacklists, finding no issues there. This can be confusing and lead to uncertainty about the cause.
• Local vs. global blocks: The distinction between a Barracuda-implemented (system-wide) block and a user-implemented (recipient-specific) block is critical for diagnosis. If not all recipients at Barracuda domains are bouncing, it's likely a user-level block.
• Content and sender issues: Even if not globally blocklisted, emails can be rejected due to problematic content or if the from address or domain is blocked by a specific Barracuda filter.
• Impact on deliverability: Bounce backs, regardless of their source, negatively impact sender reputation and overall email deliverability rates. Addressing them promptly is key to maintaining a healthy sending program.

Key considerations

• Verify extent of blocks: Determine if the bounces are isolated to a few recipients or are occurring across all Barracuda-hosted domains. This helps pinpoint if it's a specific user setting or a broader block.
• Content review: Regularly review email content for potential spam triggers. Barracuda's filters are robust, and even subtle elements can cause a block.
• Recipient engagement: Consider if recipients have manually blocked your emails. If a user has implemented a block, further sending attempts to that address will consistently bounce. This can lead to high bounce rates.
• List cleaning: If bounces persist for specific addresses, removing them from your list is advisable to maintain good sender health. This helps to prevent your domain or IP from being placed on a blocklist.Learn how to combat email bounce backs.

Key opinions

• Diagnostic approach: Experts recommend gathering more data to diagnose Barracuda bounces. The extent of the bounces (all addresses vs. some, all domains vs. some) provides crucial clues.
• Block origin: A Barracuda-implemented block often affects all addresses at all Barracuda domains, while a user-implemented block is specific to certain addresses or domains.
• Hidden causes: If Barracuda is blocking, it's frequently related to the email's content or the From: domain/address being flagged, even if not on a public blacklist.
• Permanent removal: For consistent user-implemented blocks, experts advise removing those addresses permanently from your mailing list to protect your sender reputation and avoid future issues.

Key considerations

• Collect full headers: To accurately diagnose Barracuda blocks, always try to obtain the full bounce message and email headers. This often provides more specific error codes or reasons for rejection.
• Monitor blocklists: While your domain or IP might not be on Barracuda's public blocklist, their internal systems use proprietary reputation metrics. Consistent monitoring is key. Understand what happens when you are blacklisted.
• Sender authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured. Authentication failures can contribute to Barracuda rejecting your mail, even without a direct blocklist entry.
• Engagement metrics: A decline in recipient engagement can negatively impact your sender reputation over time, leading to more aggressive filtering by systems like Barracuda. Maintaining a healthy sending pattern is vital for good domain reputation.

Key findings

• Comprehensive protection: Barracuda Email Protection leverages Barracuda Central to identify known spammers and assess if embedded domains lead to spam or malware, contributing to blocking decisions.
• Content analysis: The Barracuda Email Security Gateway allows administrators to set custom content filters based on subject line, headers, and message body. This can lead to blocks if content triggers these rules.
• Sender authentication: Barracuda's sender authentication features, including bounce suppression and checking for required TLS connections, can lead to blocks if not properly adhered to.
• Message actions: Barracuda provides various message actions, including blocking messages for reasons like 'Inbound TLS Required' if a secure connection is not used.

Key considerations

• TLS encryption: Ensure your sending infrastructure supports and uses TLS connections for outbound mail. Barracuda systems may block inbound messages without TLS if configured to do so.
• Adhere to best practices: Review and align your sending practices with general email deliverability best practices, especially concerning email authentication (SPF, DKIM, DMARC), to build a strong sender reputation that Barracuda's systems will trust.
• Spam and threat identification: Understand that Barracuda prioritizes identifying and blocking email from known spammers and phishing threats. Ensure your email content and sending patterns do not mimic these characteristics.
• Incident response: Be aware that Barracuda offers incident response capabilities to recipients, allowing them to search and identify delivered email. This means problematic emails, even if initially delivered, can be retrospectively addressed by recipients, impacting future deliverability. Review the latest deliverability challenges.