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I have a user who is using Hotmail to communicate with one of our suppliers.

Recently, Hotmail started bouncing emails to that address (while other ISPs are working fine.) Hotmail bounce messages contain very little details.

Investigating, I found that the supplier's ISP has appeared on a blacklist of ISPs who do not do enough to prevent spamming from their users. (Note: Neither my user nor the supplier are mass-mailing.)

In the circumstances, I can understand Hotmail declining to accept emails from the host, or accepting them but being quick to mark them as spam. However, I am surprised that they might refuse delivery.

Does this sound plausible to you, or am I barking up the wrong tree?

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Can you edit the post and include what you can from the bounce message? It really does help to analyze it. – Ryan Gooler Aug 27 '10 at 21:23

i might be totally wrong here, but when the spamming mail servers try to send to non existing addresses, would hotmail's servers not need to send outbound rejection messages ? - if so i guess they might have taken the steps to block those too. Seems unlikely though.

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There is a trend to not respond with or greatly reduce NDRs in response to Backscatter attack tactics. – user48838 Aug 13 '10 at 9:46

It can be a ploy to get the attention of the remote system administrators to take action. The Hotmail folks would need to address it directly.

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