Explaining non-delivery report type of spam
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.
GFI Software published a white paper to explain what NDR spam is all about and why spammers have resorted to this effective method to distribute unsolicited mail.