NDR spam explained 
(13/06/2008)
Research shows that up to 90% of emails received by companies are spam, and spammers have adopted a variety of methods to bypass spam filters used in anti-spam software. In the beginning, spam was mainly text based but over the past few years, spammers have resorted to using embedded images and attaching common file types such as mp3s and Excel documents in emails to gain access to mailboxes. Another option is NDR or non-delivery report spam.
NDRs are a common part of email exchanges. Users receive NDRs, for example, when an email does not arrive at a recipient’s address and notification is sent to the sender. However, spammers can cause a considerable increase in NDR activity because they send junk mail to thousands of email addresses. Some are genuine but others are not and these are used to generate NDR messages by manipulating the ‘From’ address to use a real domain sender. This results in email users receiving NDRs from people they had never sent an email to in the first place.
Unless action is taken, email servers could be inundated with useless emails thereby hogging system resources and affecting performance. The best way to stop NDR spam is to deploy anti-spam software that can identify spam in NDRs and delete them from the server.
A variety of technologies are used and anti-spam software like GFI MailEssentials uses Bayesian Filter, DNS Blacklists, Spam URI RealTime Blocklists and Keyword Checking to keep NDR spam at bay. GFI MailEssentials also uses a Directory Harvesting feature on the email gateway to drop email messages and NDRs sent to non-existent users.
GFI Software has launched a white paper to explain what NDR spam is all about and why spammers have resorted to this effective method to distribute unsolicited mail. This white paper explains what NDR spam is and how administrators can take effective measures to reduce the impact on their email servers.
Related topics: Internet and Web security Virus, Worm, Email security, spyware and malware
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