Backscatter and spam
This article discusses backscatter, some possible ways to help reduce it, and why there is no easy way to resolve the problem.
What is backscatter?
Backscatter is a side effect of spammers sending forged bulk messages (spam) that appear to originate from valid e-mail addresses. Spammers do this to increase the likelihood of their messages getting through filters and reaching recipients. If spammers use e-mail addresses from your domain in their forged messages, you may receive backscatter.
The following steps outline how backscatter is generated:
- The spammer generates a message that contains a forged sender (FROM) e-mail address. The sender e-mail address is real and valid (for our example, we will use the fictional e-mail address [email protected]).
- The spammer sends the forged message to a recipient e-mail address that is not on the example.com domain.
- The recipient's mail server rejects the message as spam, and sends a bounce notification to the supposed sender (in this case, [email protected]).
- Kelly's inbox at [email protected] now has a bounce notification message (“backscatter”) in it.
This example scenario describes the process for one message, but spammers will usually send many, many messages. This generates a large number of bounce notification messages, all of which in this case go to [email protected].
Because of how the SMTP protocol works, there is unfortunately no one single “fix” that can be done to eliminate all backscatter all of the time.
However, there are a few things you can do to help reduce the likelihood of receiving backscatter:
- Minimize e-mail address collection: Try to avoid posting valid e-mail addresses on your website. There are many bots that crawl web pages searching for e-mail addresses. If your site content does not contain any of your e-mail addresses, it is less likely that spammers can use them as forged sender identities.
- Enable Sender Policy Framework (SPF): Enabling SPF on your domain may help reduce backscatter, though unfortunately many e-mail servers do not actually honor SPF settings. For information about how to configure SPF for your account, please see this article.