said by joako :

It is called Backscatter

You should treat it as any other spam and report the sending server.

quote:

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The judgement call for what to do with undelivered mail is not simple. Best practice is, wherever possible, to reject the spam at the boundary and be done with it. The alternative is to discard spam that has already been received, and try to report non-delivery only to plausible senders.

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