Backscatter messages and EOP

Exchange Online
 

Applies to: Exchange Online, Exchange Online Protection

Topic Last Modified: 2016-12-09

Backscatter messages are the automated bounce messages that are sent by mail servers, typically as a result of incoming spam. Because Exchange Online Protection (EOP) is a spam filtering service, email messages sent to nonexistent recipients and to other suspicious destinations are rejected by our service. When this happens, EOP generates a non-delivery report (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 a backscatter message. When this happens, outgoing servers that are associated with the EOP network may be listed on the Backscatterer DNS Block List (DNSBL). The Backscatterer DNSBL is a list of IP addresses that send backscatter messages. It isn’t a spammer list, and we don’t try to remove our servers from the Backscatterer DNSBL.

TipTip:
According to the instructions on the Backscatterer website, the use of reject mode for all incoming mail isn’t a recommended configuration or use of that service. It should be used in safe mode instead. For more information about implementing the correct backscatter configuration, visit the Backscatterer.org website.
 
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