Why are my emails bouncing and is my sending IP on the SORBS spam blocklist?
Michael Ko
Co-founder & CEO, Suped
Published 1 May 2025
Updated 17 Aug 2025
7 min read
It's a frustrating experience: you send out an important email, perhaps to a new lead or a key client, and it bounces back. The error message is cryptic, but somewhere in the jumble, you spot a reference to 'SORBS' or another 'spam blocklist'. Immediately, your mind goes to, 'Is my sending IP on the SORBS spam blocklist? Why are my emails bouncing?' I've seen this scenario play out countless times.
The immediate reaction is often to pinpoint the blocklist (or blacklist, as they are interchangeably called) as the sole culprit. While being listed on a blocklist like SORBS can certainly impact your email deliverability, it's crucial to understand that it's often a symptom of deeper underlying issues, not just the problem itself. It's like finding a leak in your roof and realizing it's due to a much larger structural problem.
My goal here is to help you understand why your emails are bouncing, specifically when SORBS (the Spam and Open Relay Blocking System) is mentioned, and guide you through diagnosing and resolving these issues. We'll look beyond just the blocklist itself to uncover the true causes and put you on the path to better inbox placement.
First, let's clarify what a bounce is. An email bounce occurs when an email server rejects a message, preventing it from reaching the intended recipient's inbox. These rejections come with specific codes and messages that can offer valuable clues about the problem. Ignoring these bounce messages is like ignoring warning lights on your car's dashboard.
Bounces are typically categorized as either hard bounces or soft bounces. A hard bounce indicates a permanent delivery failure, often because the recipient's email address doesn't exist or the domain is invalid. A soft bounce, on the other hand, is a temporary issue, such as a full mailbox, a server being temporarily unavailable, or the email size being too large. Understanding the distinction is key to effective bounce management. You can learn more about this in our guide on why you are getting soft bounces.
When your emails bounce and the message references a blocklist (also called a blacklist), it means the receiving mail server checked your sending IP address or domain against one of these lists and found a match. This caused the rejection. The specific wording in the bounce message is often your first, best clue.
For example, you might see something like "554 5.7.1 Service unavailable; Client host [X.X.X.X] blocked using dnsbl.sorbs.net". This clearly indicates that SORBS is the reason for the bounce. For a deeper dive into these lists, refer to our in-depth guide to email blocklists.
Is my sending IP on the SORBS spam blocklist?
The Spam and Open Relay Blocking System (SORBS) is a DNS-based blocklist (DNSBL) that lists IP addresses of servers known for sending spam or operating as open relays. While SORBS has been around for a long time, its impact on email deliverability varies. Some mailbox providers use it extensively, while others give it less weight.
If your IP address or domain is listed in SORBS, it means your emails have been flagged as spam, or your server has been identified as an open relay. This can happen for various reasons, including sending to spam traps, high complaint rates, or misconfigurations. You can read more about SORBS and its listing criteria on the Coldlytics glossary page on the SORBS spam blacklist.
Direct impact
Some ISPs: Google, Yahoo!, and other providers may use SORBS to block messages, leading to bounces.
Immediate rejections: When a recipient's server consults SORBS and finds your IP listed, your email is often rejected outright.
Bounce messages: You will receive non-delivery reports (NDRs) explicitly stating the SORBS listing as the reason.
Underlying issues and correlation
Reputation indicator: A SORBS listing often signals other email deliverability problems, like poor list hygiene or sending to spam traps.
Broader impact: While some providers might not block purely due to SORBS, they may use it as one of many signals for filtering.
Hidden problems: A listing might have been active for a long time without you noticing, with actual blocking only starting recently.
The key takeaway is that while SORBS (or any blocklist) can directly cause bounces, its presence often highlights underlying issues with your sending practices or list quality. For more information on the severity of a SORBS listing's impact, see our page on how severe a SORBS listing impact is.
Diagnosing the root cause of bounces
The most effective way to diagnose the actual cause of your email bounces is to analyze the non-delivery reports (NDRs) or bounce messages you receive. These messages contain crucial details, including the specific error code and, often, the name of the blocklist that rejected your email. Your email service provider (ESP) or mail server logs should provide access to these bounce messages.
Here's a common bounce message snippet you might encounter:
Example SORBS Bounce Messageplaintext
550 5.7.1 Service unavailable; Client host [192.0.2.1] blocked using dnsbl.sorbs.net; See: http://www.sorbs.net/lookup.shtml?192.0.2.1
As you can see, the message clearly states that the block was due to dnsbl.sorbs.net. This is why examining the full bounce message is essential, rather than just relying on a general 'blocklisted' status. This approach helps you determine how to handle bounced emails more effectively.
If you're on a shared IP address, it's possible that another sender's poor practices led to the listing. In such cases, your ESP or hosting provider is responsible for addressing the blocklisting. However, if you are on a dedicated IP, the issue is directly related to your sending practices. For a more comprehensive guide on this, consider reading why your IP address is blacklisted.
Proactive measures and delisting strategies
Getting off any blocklist, including SORBS, starts with addressing the reasons you were listed in the first place. For SORBS, this typically involves ensuring your email server is not an open relay and cleaning up your sending practices. You can usually initiate a delisting request directly on the SORBS website. However, without fixing the underlying problem, you might find yourself relisted shortly after.
Here are some proactive steps to prevent future blocklistings and improve your overall email deliverability:
Maintain clean lists: Regularly remove inactive or invalid email addresses. This reduces bounces and avoids spam traps.
Implement authentication: Ensure your domain has proper SPF, DKIM, and DMARC records configured. This helps mailbox providers verify your identity.
Monitor sending reputation: Keep an eye on your sender reputation and blocklist status. Tools are available to check if your IP is on blocklists.
Manage complaints: Implement a clear unsubscribe process and promptly remove recipients who mark your emails as spam.
Send requested emails: Only send emails to users who have explicitly opted in to receive communications from you. This is the foundation of good deliverability.
For a detailed guide on handling a SORBS listing, our dedicated article What to do if your IP is blacklisted on SORBS? provides step-by-step instructions. Remember, persistent monitoring and adherence to best practices are key to maintaining a healthy sender reputation and avoiding email bounces.
Views from the trenches
Best practices
Always prioritize understanding the actual bounce message, as it often clearly names the blocking entity.
Regularly review your email lists for inactive subscribers and invalid addresses to reduce spam trap hits.
Implement strong email authentication protocols like SPF, DKIM, and DMARC to build sender trust.
Maintain consistent sending volumes to avoid sudden spikes that can trigger spam filters.
Common pitfalls
Panicking about a single blocklist listing without investigating the deeper reasons for the bounces.
Assuming a shared IP blocklist is always someone else's fault and not reviewing your own sending habits.
Attempting to delist without addressing the root cause, leading to rapid re-listings.
Ignoring bounce messages or not having a system to analyze them effectively.
Expert tips
If your ESP tells you your IP is on a blocklist, ask them for the full bounce message. This is critical for diagnosis.
A listing on an RBL (real-time blacklist) like SORBS often means you're doing other things that trigger blocks on more impactful lists. Focus on overall email health.
Sometimes, a blocklist listing can exist for a long time without causing significant impact until a recipient domain starts enforcing it.
If using shared IPs, blocklisting might be due to other senders. Communicate with your ESP.
Expert view
Expert from Email Geeks says spam filters use SORBS to block mail.
2024-01-08 - Email Geeks
Expert view
Expert from Email Geeks says for B2B senders, SORBS listings typically have a limited impact, affecting only a small percentage of emails.
2024-01-08 - Email Geeks
Moving forward with better email deliverability
In conclusion, while discovering your sending IP on the SORBS spam blocklist can be alarming, it's often a signal to investigate your broader email sending practices. Don't just focus on the blocklist entry itself.
By carefully analyzing bounce messages, understanding the nuances of different blocklists (or blacklists), and consistently applying email deliverability best practices, you can effectively resolve current bounce issues and protect your sender reputation in the long term. Proactive management of your email program is always the best defense against deliverability challenges.
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URIBL
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ALPHANET
Anonmails
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Calivent Networks
EFnet
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Scientific Spam
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System 5 Hosting
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www.blocklist.de Fail2Ban-Reporting Service
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Fayntic Services
ORB UK
technoirc.org
TechTheft
Google
, Yahoo!, and other providers may use SORBS to block messages, leading to bounces.
