GFI has released a white paper examining NDR spam. NDRs (Non Delivery Reports) are simply the “bounce back” message a sender gets when their email is rejected by the recipient’s mail server. This usually happens if the address is invalid or the sender’s has been added to a blacklist. Spammers can wreak havoc with NDRs when they send thousands of spam messages to a domain using an alphabet attack. The flood of NDRs that result consume bandwidth and resources, slowing servers down. Spammers have another trick up their sleeves as well. They forge the From: field using a legit address and this results in people getting NDR’s for messages they never sent-with the spam conveniently attached, of course!

In extreme cases this can act like a DDoS attack and cripple a server. If you maintain a server responsible for sending this backscatter, you may find your domain blacklisted, causing headaches for your users. What’s the solution? If your server is on the receiving end, turning off any catch all addresses is a smart move. On the other end? Configure your server to reject during STMP transmission. Another way to fight backscatter is with an anti-spam solution that detects spam in NDR’s and deletes them from the server. One of these is the award winning MailEssentials program by GFI. It’s the number 1 anti-spam filter on the market. To learn more, read GFI’s NDR spam white paper and make an informed decision for your business.