On Monday, August 15 2016, some email senders started noticing an increase in the amount of IP addresses being blacklisted by the anti-spam organization Spamhaus. The Spamhaus SBL listings were the result of “Abused/ misconfigured newsletter service” as the result of spammers and malicious people “subscription bombing” newsletter signup forms.
In these cases, a large number of government addresses from different countries were subscribed through the newsletter sign up form by the use of a script/bot or an automated process. This resulted in those email addresses receiving hundreds—if not thousand—of opt-in confirmation email as well as marketing email.
Laura Atkins of WordToTheWise.com posted three great blog articles giving a summary of the issue, comments from Spamhaus CEO, Steve Linford and a followup article about the ongoing attack from security reporter Brian Krebs.
Whether you have received a Spamhaus SBL listing on your sending IP addresses or not, Return Path recommends reviewing all subscribers that you acquired in August, to ensure you have not been a victim of subscription bombing.
Some of the areas to review:
If you are seeing subscribers signing up from the same IP addresses or the same email addresses signed up to multiple mailing lists you should consider blocking those subscribers—doing so could prevent a future Spamhaus SBL listing.
So, what are some things that senders can do to prevent their sign up forms from being abused?
If you have any questions about preventing sign up abuse or about dealing with a Spamhaus blacklisting please reach out to your Return Path Technical Account Manager and they would be happy to help you.
Kent McGovern is a Client Support Manager at Return Path. Leveraging almost a decade in the email optimization industry he helps senders with their most difficult deliverability challenges such as authentication and blacklist mitigation. When he is not going through bounce logs and email headers you can usually find him on a pool table or playing video games.
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