User flooded with Undeliverable messages - ORF Forums

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One of my users have been receiving hundreds of "Undeliverable" messages every week for over a month. It happened to this user and to a few others before and it usually just stops after a day or two. But not this time.

I understand this means some spammer is using his e-mail address as the reply-to address on spam e-mails but I'd like to know what the best plan of action would be? I don't think the keyword filter would work as it would block legit "Undeliverable" messages and also because these messages have different subjects and are in dozens of languages.

We're on Exchange 2003.
Changing his e-mail address isn't a possibility.


by PL 8 years ago

@PL: This is called email backscatter: a spammer spoofs your user's email address, and the spam target recipient servers floods the user with NDRs (of emails he/she never sent actually). For solutions, please read our article at

by Krisztian Fekete (ORF Team) 8 years ago
(in reply to this post)

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