Have you been blocked?
All blocklists are researched and managed by The Spamhaus Project.
Simply click on the link below, which will take you to the Project’s IP and Domain Reputation Checker. From here you will be able to enter your IP or Domain and begin your request for removal.
Please note that the Project’s IP and Domain Reputation Checker is the only place where removals are handled.
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Posted by The Spamhaus Team on 15 Feb 2022
A hard bounce occurs when the email server rejects the email due to permanent conditions. This typically results when ‘user unknown’ or ‘domain not found’ errors occur. However, there are also other, less common reasons.
The SMTP response code for all hard bounces begins with 5xx. Below are some of the most frequently seen by marketers:
In relation to an email marketing campaign, most of these errors are the direct result of poor data hygiene. As there is a considerable amount of churn in email addresses, sending to outdated lists increases the chances of sending to non-existent domains. This can be dangerous as non-existent domains can be spamtraps. If you encounter a hard bounce, ensure you don’t send to the contact again.
A soft bounce occurs when the email server rejects the email due to a normally temporary condition, such as a full inbox or too many complaints. When that happens, the system tries to send the email again until it is either accepted or times out. The time-out is set on the sending side and varies by network.
Some ISPs respond to dips in reputation by issuing “tempfails” preceded by a 4xx code, usually 421. This means they will defer mail for a determined amount of time until either the mail stops coming or reputation re-calculates upward again. That error can look like this: “421 4.7.0 [TS01] Messages from x.x.x.x temporarily deferred due to user complaints.”
Addresses affected by a temp-fail should not necessarily be removed from a mailing list! If the block is due to a poor-quality mailing list, you should review your list hygiene and correct any problems before trying again.
In the modern email ecosystem, most receivers base their spam filtering on a reputation-based system, be it purchased, home-grown, or a combination of the two. They all have different ways of accomplishing their goal of protecting their users from unwanted email, but they all have some commonalities. ISPs typically respond to mail that is coming from an IP/domain with poor reputation and/or incorrect or missing authentication in this general pattern:
If an ISP issues a hard block, they are indicating they will no longer accept mail from the sending IP and that this is not a temporary issue. The most commonly used SMTP code for hard blocks is:
This type of bounce occurs when the receiving email server rejects the email for policy reasons, including:
Depending on the ISP, the blocks will often disappear over an arbitrary period (24-72 hours, generally) if the triggering issue ceases.
The error for such a block will usually begin with “554” and contain more specific information or a URL you can consult for more details. For example: “554 The IP address of your mail server (127.0.0.1) was found in the Spamhaus blocklist. See https://check.spamhaus.org/ for details“.
These blocks can result from a decision made by looking at their own data, data provided by a reputation provider like Spamhaus, a filter vendor such as Cloudmark, or a combination of two or more of these.
If the block does not resolve on its own, but you have resolved the triggering issue, you will need to open a ticket with the network that is issuing the block to fix the problem, if possible. It will be necessary to understand what caused the block and correct it before opening a ticket. Some ISPS, notably Gmail, have no remediation path available at all.
Correctly managing bounces goes a long way toward keeping mailing lists clean and up to date.
As a general rule, it is safe to say that Gmail, Hotmail, and Verizon Media (what used to be Yahoo and AOL) use mostly home-grown spam filtering technology. Due to the nature of their business model as mailbox providers, they have access to a huge amount of data regarding their own users’ email behavior. Generally, these providers prefer to use their data, as it is more accurate in relation to their networks. They may or may not use commercially available data combined with their own: they will not say.
Providers like Comcast, RoadRunner, and Sky use commercial spam filters and reputation providers such as Cloudmark’s and Spamhaus’ offerings.
Modern spam filters have become very sophisticated; they are flexible and fast. Being blocked by any spam filter vendor (such as Cloudmark) or reputation provider (such as Spamhaus) can have time-consuming and costly results.
Of course, the impact depends on many factors, including how widespread the adoption of the filter is. There are hundreds of blocklists in the industry, but only a few have a broad impact. Even if you use a comprehensive blocklist checking tool to review your IP or domain (MXToolbox, for example), you will end up on a blocklist somewhere. How seriously to take that depends on who is issuing the block. For example, a listing on the Spamhaus SBL has enormous reach, whereas you can happily ignore a listing by SPEWS.
Now you know how to handle bounced emails let’s review how to manage complaints.
16 August 2022
The recent spate of informational listings from The Spamhaus Project researchers created waves in the sending community. But more pertinently, it’s highlighted poor sending practices. Here’s further explanation, and helpful hints and tools to help calm the waters.
15 February 2022
Here's our guide to email frequency & engagement, helping you understand how often to email contacts and keep them engaged for email deliverability.
Monitoring email complaints is a vital piece of the reputational “pie," so keeping them as low as possible should be every marketer's goal.