554 5.1.0 Sender Denied

When an email sender reports a delivery failure message 554 5.1.0 Sender Denied it will be related to the filtering features available in Microsoft Exchange.

Example delivery failure notification received by sender

Example delivery failure notification received by sender

Depending on the version of Exchange this can simply be a denied sender list or it may be related to the Safelist Aggregator that is available in Exchange 2010 and Exchange 2013.

http://technet.microsoft.com/en-us/library/bb125168(v=exchg.150).aspx