How to prevent SpamHaus SBL (Spamhaus Block List) blacklisting in web hosting servers

How to prevent SpamHaus SBL (Spamhaus Block List) blacklisting in web hosting servers

554 5.7.1 Service unavailable; Client host [154.0.***.**] blocked using;
SMTP error from remote mail server after pipelined DATA:
    550-197.242.**.*** listed at

You’d seen these error messages in your mail server, if your IP address has ever got listed in Spamhaus SBL. Getting blacklisted in SBL is a concern for many web hosts, as it often leads to customer complaints about mail delivery failures.

Our engineers fix Spamhaus issues everyday in their role as Outsourced Support Specialists for web hosting providers. Since Spamhaus checks only for their SPAM criteria, we’ve seen that even perfectly legitimate business mails were tagged as spam.

If not monitored closely or not taken proper preventive measures, chances are that the IP gets listed again, soon after delisting it. Sr. Support Engineer Hamish explains:

“SBL blacklisting often happens without a warning or grace period. Spamhaus SBL lists are updated every 10 minutes, and many a times, web hosts know about the blacklisting only when users complain about email bounces. If not delisted promptly, the IP can remain in the list for about 6 months, affecting mail delivery over this entire period. ”

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What is SpamHaus Block List (SBL)?

Spamhaus Block List (“SBL”) is a database of IP addresses which are marked as direct or supportive sources of spam, based on Spamhaus’s criteria.

The causes for SBL block can be broadly categorized into two – 1. Your mail server sending out spam directly 2. Your server gets being labeled as a source of spam indirectly.

In direct spamming, spam mails originate from your servers and is sent to other mail servers.

“Spammers or attackers can use your mail servers to send out spam”, says Hamish. “Vulnerable software or malicious scripts can be the source of such spamming. Valid users sending out unsolicited bulk mails from your server can also cause it to be blacklisted.”

Your mail server can get listed as spam due to its indirect involvement with spammers.

“Massive spamming that involves multiple IP address in a network can end up blacklisting the entire IP range.”, Dileep adds on. “If your server happens to be in that range, you’d be blacklisted too. Spam traps that get accidentally added to user mailing lists in your server is another reason for blacklist.”

Many mail servers use Spamhaus SBL to verify whether an incoming mail is from a sender whose IP is blacklisted or not. Mails from servers listed in SBL are rejected, as a preventive measure to combat spam.

That’s why getting listed in blacklist is not a good thing for web hosts, as it would directly affect your server reputation and cause trouble to the valid customers who use these mail servers to send mails.

So, why do you get blacklisted even if you don’t send out spam mails?

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How does your server get listed in SBL even if you are not sending out spam?

SBL is updated every 10 minutes, and without even verifying the content of the mails. Spamhaus has its own definition for spam, and this criteria is focused more on the consent of the receiver, than its content.

If an email is unsolicited and sent in bulk (UBE), then the message is treated as spam by Spamhaus. Servers who have users sending out such mails would be considered as spammers and added to SBL.

Bobcares Support Engineer Dileep explains:

“Web hosts often have users sending out bulk emails as a part of their business promotions, inquiries, etc. But these ‘legitimate’ mails can cause your server IP to end up in the SBL. Once listed, these records would remain intact for a long period. That’s why it is crucial for web hosts to act promptly and get the IP delisted to ensure seamless mail delivery.”

So, what’s the solution?


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Bobcares is a server management company that helps businesses deliver uninterrupted and secure online services. Our engineers manage close to 51,500 servers that include virtualized servers, cloud infrastructure, physical server clusters, and more.