Backscatterer — Check, Delist & Monitor

Overview

Backscatterer.org operates a specialized blacklist that detects a single, specific problem: backscatter. Backscatter occurs when a mail server accepts an email, determines that the recipient does not exist (or that the message should be rejected for another reason), and then generates a bounce message (Non-Delivery Report / NDR) back to the sender address. Because spammers routinely forge sender addresses, these bounce messages end up hitting innocent third parties who never sent the original email.

This is a fundamentally different problem from spam sending. A server on the Backscatterer list is not necessarily sending spam — it is sending misdirected bounce messages because of a configuration flaw. The fix is almost always the same: configure the mail server to reject invalid recipients during the SMTP transaction (at the RCPT TO stage) rather than accepting the message and generating a bounce after the fact.

The most common culprits are catch-all mailboxes, legacy mail servers that accept-then-bounce, and forwarding configurations that generate NDRs when the destination server rejects the forwarded message. Each of these can be fixed with straightforward configuration changes.

Backscatterer listings auto-expire after approximately 4 weeks once the backscatter stops. There is no express removal process or payment option. The 4-week window is intentionally long to ensure the underlying problem has been genuinely resolved rather than temporarily masked.

While the Backscatterer list is not used by major mailbox providers like Gmail or Microsoft, it is referenced by a meaningful number of independent mail administrators and smaller hosting providers. More importantly, a Backscatterer listing is a clear indicator that your mail server has a configuration problem that should be fixed regardless of its impact on delivery.