Users in a Microsoft Forefront Online Protection for Exchange (FOPE) environment receive a non-delivery 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:
- The FOPE outgoing (also known as "outbound") edge servers are listed in the Backscatterer.org reputation block list. This listing cannot be prevented because of certain kinds of spoofing attacks that can be tried against the FOPE service and our customers.
- The recipient email environment implemented the Backscatterer.org service in reject mode instead of in safe mode.
- The recipient email environment has not added the FOPE outgoing edge server IP addresses to the list of allowed mail senders.
It is very common for FOPE outgoing edge servers to be listed by BackScatterer.org. However, if you have to verify this, follow these steps:
- Use the Message Trace feature in the FOPE Administration Center to determine the host name of the outgoing edge server that sent the customer’s mail item. For more information about how to run a message trace, visit the following Microsoft TechNet website:
- Use the test provided by BackScatterer.org service to determine if the IP Address is listed as source of SPAM.
Because the cause of the issue is rooted in the Backscatterer.org service, the resolution must be directed at Backscatterer. Microsoft Online Services does not support Backscatterer.org services. The following guidance is provided as-is and without any warranty to remedy 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:
- Contact the recipient email administrator to have the following FOPE outgoing edge server IP addresses added to an allow list to bypass the Backscatterer.org checks.
Backscatter (also known as outscatter, misdirected bounces, blowback, or collateral spam) is the incorrect and automated bounce messages that are sent by mail servers, typically as a side effect of incoming spam. Because FOPE is a spam-filtering service, mail to nonexistent recipients and to other suspicious messages is rejected by our service. When that happens, FOPE 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 FOPE network may be listed on the Backscatterer DNS block list (DNSBL).
The Backscatterer DNSBL is a list of IP addresses that send backscatter. It is not a spammer list. According to the instructions on the Backscatterer website, the use of reject mode for all incoming mail is not a recommended configuration or use of that service. It should be used in safe mode to block messages where MAIL FROM
is the following:
For more information about the correct configuration, visit the following Backscatterer.org website:
Microsoft is committed to enabling customers to have a secure email environment that is both spam-free and virus-free. As part of that commitment, FOPE takes many steps to make sure that mail that is filtered through our network does not contain unsolicited commercial messages.
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