The sender is receiving a bounce back with the error "550 5.7.1 Message rejected as spam by Content Filtering"
Error: "550 5.7.1 Message rejected as spam by Content Filtering"
Exchange server have built in filtering features that can block certain emails if they match their content filtering rules. Email messages that are empty in content ( or nearly empty) may be caught by one of the default filtering options turned on in Exchange 2007/2010. This error is generated by the default-enabled Content Filtering anti-spam option under Hub Transport>Anti-Spam.
Steps to resolve the issue
From the Exchange program group:
Open the Exchange Management Console. Next, depending on the server type, select either of the two options below - Microsoft Exchange | Edge Transport | Anti-Spam - Microsoft Exchange | Organization Configuration | Hub Transport | Anti-Spam All of the filter types are enabled by default
Open the Content Filtering Anti-Spam filtering type and go to the Action tab.
Then uncheck the box next to "Reject messages that have SCL rating greater or equal to:"
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