Article ID: 2590562 - View products that this article applies to.
Users in a Microsoft Exchange Online Protection environment receive a nondelivery report (NDR) when they send email messages to a recipient whose messaging environment uses the Backscatterer.org service for mail security.
This issue occurs if all the following conditions are true:
Because the cause of the issue is rooted in the Backscatterer.org service, the solution must be directed at Backscatterer. Office 365 doesn't support Backscatterer.org services. The following guidance is provided as-is and without any warranty to resolve unexpected mail rejections from recipient environments that use the Backscatterer.org service as a block list.
To resolve this issue, try one of the following methods:
"Backscatter" (also known as "outscatter," "misdirected bounces," "blowback," and "collateral spam") refers to the incorrect and automated bounce messages that are sent by mail servers, typically as a side effect of incoming spam. Because Exchange Online Protection is a spam-filtering service, mail to nonexistent recipients and to other suspicious messages is rejected by the service. When that happens, Exchange Online Protection generates a new NDR message and delivers it back to the "sender." Because spammers frequently use a forged or invalid "from" address in their messages, the sender address to which the NDR is sent may result in backscatter. When this happens, outgoing servers that are associated with the Exchange Online Protection network may be listed on the Backscatterer DNS block list (DNSBL).
The Backscatterer DNSBL is a list of IP addresses that send backscatter. It's not a spammer list. The instructions on the Backscatterer website recommend that you not set up or use the reject mode for all incoming mail from the service. You should use the service in safe mode to block messages in which MAIL FROM resembles the following:
<>For more information about the correct configuration, see the following Backscatterer.org website:
http://www.backscatterer.org/?target=usageWe are committed to enabling customers to have a secure email environment that is both spam-free and virus-free. As part of that commitment, Exchange Online Protection takes many steps to make sure that mail that's filtered through our network doesn't contain unsolicited commercial messages.
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