Is SORBS an important email blocklist for deliverability?

Key findings

• Past relevance: While hosting companies sometimes downplayed its importance, SORBS was historically used by some business-to-business (B2B) systems for email filtering.
• Limited B2C impact: Major Business-to-Consumer (B2C) email providers like Gmail, Hotmail, and Yahoo typically did not show significant deliverability changes due to SORBS listings, although they might have used it as one of many data inputs.
• Operational focus: SORBS primarily listed IP addresses and domains associated with open relays or those that generated spam trap hits, indicating compromised or misconfigured mail servers.
• Proofpoint connection: SORBS operated as a non-profit division of Proofpoint, sharing some spam trap feeds, though Proofpoint's main reputation service used different, often more stringent, listing criteria.
• Current status: As of June 2024, SORBS has shut down, meaning it is no longer an active blocklist impacting email deliverability.

Key considerations

• No current impact: Since its shutdown, a SORBS listing no longer directly impacts your email deliverability or sender reputation. Any tools showing a current SORBS listing are outdated.
• Importance of other blocklists: While SORBS is gone, major blocklists like Spamhaus and URIBL remain critical for email deliverability. Regular monitoring for listings on these continues to be essential.
• Underlying issues: If you faced a SORBS listing in the past, the underlying cause, such as an open relay or spam trap hits, indicates deeper email hygiene issues that still need addressing. These issues can lead to listings on other active blocklists.
• Proactive hygiene: Maintaining good sender practices, including proper email authentication (SPF, DKIM, DMARC) and list hygiene, is key to avoiding current blocklists and ensuring healthy domain reputation.

Key opinions

• Initial concern: Marketers frequently experienced anxiety and confusion when their IP or domain appeared on SORBS, especially if they were not dedicated email marketers but rather ordinary businesses.
• Hosting company reassurances: Many marketers received assurances from their hosting providers that SORBS was not widely used by ISPs for filtering, though this often contradicted their own perception of the blacklist's importance.
• Shared IP challenges: A common scenario involved shared IP addresses on hosting platforms, where a SORBS listing for one user could impact others on the same IP.
• Desire for correctness: Despite potentially low direct impact, businesses often wished to ensure their email infrastructure was properly configured and off all blocklists, including SORBS.

Key considerations

• Understand bounce messages: If you experienced issues related to SORBS in the past, checking bounce messages was a key way to determine its actual impact on specific recipients, as only directly rejected emails indicate a problem.
• Focus on major blocklists: Now that SORBS is defunct, prioritize monitoring and maintaining a clean status on the most impactful blocklists that directly affect the majority of recipient mailboxes, such as Spamhaus.
• Shared IP management: If using shared IP infrastructure, regular communication with your hosting provider about IP reputation and proactive measures remains important, irrespective of SORBS.
• Email authentication: Ensure your sending domains have proper SPF, DKIM, and DMARC records configured, as these are far more critical for modern email deliverability than legacy blocklist concerns.
• Deliverability impact: While a minor blocklist might not severely impact deliverability, a listing on any blocklist for legitimate senders means an underlying problem. Always investigate and resolve these issues to protect your sender reputation.

Key opinions

• Variable impact: Experts noted that SORBS's impact varied, causing only a few percentage points' rise in bounces for business-to-business (B2B) clients but almost no change for major Business-to-Consumer (B2C) providers like Gmail, Hotmail, or Yahoo.
• Input, not primary filter: While large providers like Google might have consumed SORBS data, it was typically just one of many inputs into their complex filtering systems, not a primary blocking factor.
• Ownership and criteria: SORBS was a non-profit division of Proofpoint, sharing some spam trap feeds. However, Proofpoint's own appliances used a separate reputation service with different, more robust, listing criteria.
• Causes of listing: Experts primarily dealt with SORBS listings due to spam trap hits, rather than solely open relays, requiring submission of tickets and analysis of redacted headers for resolution.

Key considerations

• Delisting feasibility: Despite a listing's perceived importance, delisting from SORBS was generally considered a low-effort process, often achievable even for shared IP addresses, by engaging with the SORBS team directly.
• Prioritize major blocklists: Deliverability experts consistently point to Spamhaus and URIBL as the most significant blocklists to avoid, as they carry far more weight with major ISPs.
• Focus on root causes: Any historical SORBS listing, whether due to open relays or spam traps, signifies a need to address underlying mail server configurations and list hygiene to prevent future deliverability issues on other active blocklists. Tools like DNSBL checks can help identify these.
• Continuous monitoring: Regularly monitoring your IP and domain reputation on active, influential blocklists is far more beneficial than dwelling on historical (or defunct) ones like SORBS. Spamresource.com offers excellent resources on this.

Key findings

• Original purpose: SORBS (Spam and Open Relay Blocking System) was designed as an anti-spam project to identify servers sending email via proxy and open-relay servers through real-time checks.
• Listing criteria: It listed IP addresses and domains known for spamming or having open relays, acting as a database for email servers with problematic histories.
• Long operational history: SORBS operated for over two decades, signifying its long-standing presence in the anti-spam landscape.
• Cessation of operations: As of June 2024, SORBS officially shut down, effectively ending its role as an active blocklist.

Key considerations

• Historical context: Understanding SORBS's historical function highlights the evolving nature of email security and the continuous effort to combat spam, as detailed in guides like A brief history of email blacklists.
• Focus on active threats: With SORBS no longer active, email senders should now prioritize adherence to best practices and monitoring their standing on currently active and influential email blocklists.
• Importance of reputation: Regardless of specific blocklists, maintaining a strong sender reputation is crucial. Blocklists for both IP addresses and domains can still severely impact reputation and deliverability, as noted by platforms like Klaviyo.
• Beyond blocklists: Modern email deliverability relies heavily on factors beyond just blocklist presence, including engagement rates, proper email authentication, and content quality. These factors determine whether emails successfully reach the inbox.