Infrastructure
What is Backscatter (Collateral Spam)?
Misdirected bounce messages or auto-replies sent to an innocent address that was forged as the sender of spam.
Backscatter occurs when a receiving server accepts a message and only later generates a bounce or auto-reply, sending it to the forged envelope sender or From address rather than the real spammer. Because spammers forge other people's domains as the return path, those bounces flood victims who never sent anything. Servers that bounce after accepting, rather than rejecting during the SMTP session, are the primary source.
Why it matters for cold email
If your domain is forged, a flood of backscatter can land you on blocklists and pollute your reputation even though you sent nothing, which is one reason a strict DMARC policy and correct SPF matter for cold senders. On the receiving side, rejecting bad mail during the SMTP conversation instead of bouncing afterward prevents your own infrastructure from emitting backscatter.
Related terms
Stop guessing at deliverability.
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