Article from Ron Edison, Founder and CTO of Internet Defense Technology
What is backscatter? These are bounces generated by spam that is sent with forged return paths (as most spam is). The bounces return to the actual owner of the email address. A great deal of backscatter returns to email addresses that don’t actually exist due to the fact that spammer’s use random/guessed email address as the return path. (The return path and from line of an email are often the same.)
While nothing really prevents spammers from originating the messages in today’s Internet, there are several measures that can be taken to minimize backscatter provided one is using domain-based email (not a yahoo.com, gmail.com, or any other ISP based email address):
1. Disable a catchall, if it exists: catchalls are a magnet for spam in general and simply accumulate huge quantities of traffic. It sooner or later becomes impractical to sort through such traffic manually thus negating any perceived benefit of a catchall. It is far better to simply return emails to incorrect addresses back to the sender as undeliverable. This also prevents a great deal of backscatter as the majority of it will be to addresses that don’t exist.
2. Use a service or server based anti spam system. Such systems employ measures that block spam and are hardened to large quantities of spam and will provide some protection from backscatter in and of themselves, however the spam protection must be implemented on the gateway to be effective in this. See our white paper for details as to why this is.
3. If the backscatter is a major problem (large quantities), and antispam service can customize rules to block it out, but not all services offer this.
Using Total Mail Defense makes possible all 3 of the above options, of course.