Your company subscribes to the Office 365 Enterprise E1 plan. You are the Microsoft Exchange Online
administrator.
In the last week, employees have reported that they are receiving non-delivery report messages from other
companies. The employees have not sent messages to recipients within those companies.
You need to prevent non-delivery report messages from reaching employees.
Which content filter option should you turn on in the Exchange admin center?

A.
NDR backscatter

B.
Conditional Sender ID filtering: hard fail

C.
SPF record: hard fail

D.
Block all bulk email messages

Explanation:
The non-delivery report messages the users are receiving are the result of Backscatter.
Backscatter is 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 the 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.
http://blogs.technet.com/b/exchange/archive/2014/08/18/spam-email-and-office-365-environmentconnection-and-content-filtering-in-eop.aspx