Blacklists or Blocklists Every B2B Enterprise Email Marketer Should Avoid

By Chris Arrendale

Published on 9 Nov, 2021

Being blacklisted or blocklisted causes major issues for one’s sending reputation. A poor reputation means an entire company may be blocked from seeing your emails and that could cost you your next million dollar deal. 

While we only mention SpamCop, SORBS, and Spamhaus in this blog post, many more spam-reporting services exist on the web. Many blocklists will block IP’s and/or domains, so strive hard to understand email deliverability best practices regarding blocklist-related issues.


The Spamhaus Project, an international organization based in both London and Geneva, tracks email spammers and spam-related activity.

Their organization maintains a “block” list of senders who have bad sending reputations. This list contains senders who have shown poor sending practices such as sending spam to Spamhaus’ partners or to their spam traps. Spamhaus will remember their IP and/or domain and publicly post them. Internet service providers and email servers use Spamhaus’ block list to reduce the amount of spam their users receive. To have stronger email delivery, verify emails are not on these blocklists.

If Spamhaus has a certain IP or domain on its list, that specific IP or domain has shown prolonged poor-sending practices. While on Spamhaus, its B2B and B2C deliverability will be significantly diminished. Yahoo, AOL, and Hotmail––as well as dozens of ISPs in Europe and uncountable corporate email servers––use Spamhaus. No other blocklist comes close to affecting this volume, making Spamhaus a top priority for monitoring and remediating.

SORBS (Spam and Open-Relay Blocking System)

SORBS has a blocklist of more than 12 million host servers known for disseminating spam, phishing attacks, and other forms of malicious email. More than 200,000 corporations worldwide use SORBS, making it a significant concern for B2B senders.

SORBS uses partner spam reports and spam traps to identify and list IP addresses that show bad sending practices. In addition, anyone can recommend a sender be put on SORBS. Fortunately, in an effort to reduce false positives (senders who are careless and not malicious), SORBS will remove offending IPs on request after 48 hours of no spam. However, repeat listings will lengthen the delisting time, and SORBS will eventually stop delisting a repeat offender.

SORBS has a low false-positive rate, making it very popular, and therefore, a top priority for monitoring and remediation––especially for B2B senders.


SpamCop is an email spam reporting service. If someone sends unsolicited bulk or commercial emails, the recipients have the option to report the IP address to SpamCops analysis. Then, SpamCop adds the IP address to their block list. Simply put, an IP joins SpamCop’s block list based on complaints of spam from that IP.

While filing spam reports, network administrators who use SpamCop will receive a list of IP addresses that are not allowed access into networks. So if someone tries sending email to an ISP that uses SpamCop from a computer whose IP is on their block list, the mail will be blocked and not delivered.

It takes upkeep to unblock IP addresses from SpamCop. Mainly, because they handle blocking and unblocking on their own. If SpamCop continues to receive reports of spam originating from the same networks responsible, those networks will continue to be listed. However, if the IP keeps up with deliverability best practices, then SpamCop will automatically delist it after 24 hours.

SpamCop, SORBS, and Spamhaus are only three of many spam-reporting services on the web. Follow email deliverability best practices to prevent being blocklisted. Keep a clean list while updating hygiene continuously, stay on top of bounce logs, and keep an eye on the content sent out. 

If you’re having deliverability problems, contact our Shift Paradigm deliverability experts.

Written By Chris Arrendale

Founder of Inbox Pros (acquired by Trendline/Shift Paradigm in July of 2018). Author of Deliverability Inferno. Certified expert and frequent speaker on the topics of data privacy, deliverability and compliance. BA in Poli-Sci/Soc from Emory, MS in Software Engineering & IT from Southern Polytechnic State University. A shoe and wine collection that’s the envy of pro athletes. Follow Chris on LinkedIn
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