Cannot send email to a distribution list

Issue: Customer called to inform that she was getting the error below when sending to a distribution list in Exchange server. User's mailbox is homed on another mail server

Your message wasn't delivered because of security policies. Microsoft Exchange will not try to redeliver this message for you. Please provide the following diagnostic text to your system administrator.

Resolution:

1. Find the Distribution list in Exchange using the mgmt console

2. Right click on it, properties, mail flow settings

3. Double click on Message delivery restrictions

4. Uncheck require that all senders are authenticated box and click ok

5. You have now resolved the issue