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550 550 5.1.1 or 550 5.7.1 NDR message when an external user sends an email message to a Universal Distribution Group
Article ID: 2773786 - View products that this article applies to.
Assume that you create a mail-enabled Universal Distribution Group in Microsoft Exchange Server 2007 or Microsoft Exchange Server 2010. When you try to send an email message from an external domain to this Distribution Group, you receive a non-delivery report (NDR) message together with one of the following error codes:
550 550 5.1.1 User unknown (state 14)
550 5.7.1 RESOLVER.RST.AuthRequired; authentication required
This issue occurs because the Require that all senders are authenticated option is enabled on the Distribution Group. By default, this option is enabled for any new Distribution Groups that are created in Exchange 2010 or Exchange 2007.
To resolve this issue, use one of the following methods, as appropriate for your situation.
Method 1: Use Exchange Management Console
Method 2: Use Exchange Management Shell
This issue does not occur for Distribution Groups that are migrated from a legacy version of Exchange to Exchange Server 2007 or Exchange Server 2010. For more information about Recipient Restrictions, please go to the following Microsoft website:
Understanding Recipient Restrictions
Article ID: 2773786 - Last Review: November 8, 2012 - Revision: 1.0