Problem

What is a DNSBL?

Solution

SORBS stands for Spam and Open Relay Blocking System. It is a DNS-based blocklist (DNSBL) service operated by Proofpoint Inc. (formerly GFI Software prior to its acquisition in July 2011) that maintains a database of IP addresses and hosts associated with spam, phishing, open relays, and other malicious email activity.

When a mail server receives an inbound email, it can check the sender’s IP against SORBS in real time. If the sending IP appears on the SORBS list, that email may be rejected, flagged, or otherwise penalised by receiving servers, thereby harming deliverability.

Brief History & Evolution

• SORBS originated in 2001 as an anti-spam project designed to monitor suspicious email sources, proxy servers, and open-relay hosts.
• Over the years it has grown in scope to include multiple categories (spam source, dynamic IPs, open proxies, etc.).
• In 2011, Proofpoint acquired the SORBS infrastructure, bringing it under a broader email security umbrella.

Why Being Listed on SORBS Matters

• Deliverability Issues: If your mail server’s IP is on a SORBS list, many recipient mail systems may refuse emails, route them to spam, or apply heavy filtering.
• Damage to Reputation: Being listed signals poor sending practices, which can affect relationships with ISPs, email providers, and customers.
• Automatic Blocking: Some email systems are configured to automatically reject or block SORBS-listed IPs.
• Cascade Effect: If your IP is blocked, even legitimate emails may fail, causing bouncebacks or non-delivery.

SORBS Categories & Listings

SORBS maintains multiple sublists. Some common ones include:

Each category has different triggering criteria and removal procedures.

How To Check If You’re Listed

1. Go to the SORBS lookup page and enter your IP or domain.
2. If listed, you will see which specific SORBS list your IP appears on.
3. Review the cause or notes provided by SORBS (some listings include timestamps or rationale).

Steps to Delist from SORBS

If your IP or domain is listed, here’s what you should do:

1. Investigate the Cause
   • Check your mail logs for signs of spam, compromised accounts, or misconfigured relay.
   • Ensure your server (and all clients) require authentication and cannot be used as an open relay.
2. Remediate
   • Secure any compromised accounts.
   • Close or restrict open relays and proxies.
   • Implement rate limiting, DKIM, SPF, DMARC, strong passwords, and monitoring.
3. Request Delisting
   • Visit the SORBS delist or removal page relevant to the list you’re on.
   • Submit a delist request, often including evidence that the issue has been resolved.
   • Note: Delisting is not always immediate, and SORBS may impose waiting periods or conditions.
4. Monitor and Maintain
   • Monitor mail traffic for anomalies.
   • Periodically recheck whether your IP returns to the list.
   • Adhere to email sending best practices to avoid relapse.

Best Practices to Avoid Future Listings

• Always configure your mail system properly (no open relays, enforce authentication).
• Use consistent, legitimate sending patterns; avoid sudden spikes in outbound email.
• Maintain good list hygiene—remove inactive or bouncing addresses.
• Implement SPF, DKIM, DMARC and properly configure reverse DNS (PTR records).
• Monitor your IP's reputation continuously using tools or services.
• Stay alert to signs of compromise or abuse (e.g. accounts sending spam).

Is SORBS the Only Concern?

No, SORBS is just one among several DNS blacklists. Others include Spamhaus, Barracuda, SpamCop, and more. Being clear of SORBS does not guarantee full deliverability; you must maintain a clean reputation across multiple services.

How Prolateral Helps

With outMail from Prolateral, you can leave blacklist worries behind and enjoy reliable, secure email delivery that just works.

outMail is built to optimise your sending reputation and keep your communications flowing smoothly even when traditional mail servers struggle.

Here’s how outMail protects and enhances your email performance:

• Automatic Reputation Monitoring: outMail keeps track of your sending IPs and domains, alerting you to any potential blacklisting on SORBS or other major DNSBLs.
• Built-In Deliverability Management: outMail routes messages through trusted, reputation-safe relays designed to maintain consistent inbox placement.
• Expert Configuration & Compliance: Our specialists handle the technical setup, including SPF, DKIM, DMARC, and reverse DNS, ensuring your mail meets best-practice standards.
• Continuous Protection: outMail proactively manages your outbound mail flow to prevent issues before they affect your business.

If you’re tired of fighting blacklists or struggling with blocked mail, switch to outMail today, the smarter, more reliable way to send business email.