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
Original KB number: 2773786
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.
Resolution 1: Use Exchange Management Console
- Click Start, click All Programs, click Microsoft Exchange Server 2010, and then click Exchange Management Console to open Exchange Management Console.
- In the Exchange Management Console tree, click Recipient Configuration, and then click Distribution Group.
- In the result pane, right-click the affected Distribution Group, and then click Properties.
- On the Mail Flow Settings tab, click Message Delivery Restrictions, and then click Properties.
- Clear the Require that all senders are authenticated option check box, and then click OK.
- Force replication among the domain controllers.
Resolution 2: Use Exchange Management Shell
Click Start, click All Programs, click Microsoft Exchange Server 2010, and then click Exchange Management Shell to open Exchange Management Shell.
Type the following cmdlet, and then press Enter:
Set-Distributiongroup -identity "Distribution group name" -RequireSenderAuthenticationEnabled $false
This issue doesn't 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, see Understanding Recipient Restrictions.