Distribution lists are used often, primarily because they are easy to manage and time efficient. By default whenever you create a distribution list (DL) it is set only to accept messages sent from authenticated users. This basically means that the distribution list is exclusively for internal mail; mail cannot be received from anyone outside the company.
When external, non-authenticated users attempt to send to a DL, they are prompted with the error message below:
#550 5.7.1 authentication required
It is clear from the error message that the issue is related to authentication. External users who are not authenticated are unable to send to a DL. To bypass this DL issue follow the 6 easy steps below:
1- Open your Exchange Management Console (EMC)
2- Click on “Distribution Group”, under Recipient Configuration
3- Right click on the desired Distribution Group
4- Double click on “Message Delivery Restrictions”
5- Uncheck the option “Require that all senders are authenticated”, then click OK
6- Restart Microsoft Exchange Transport for the changes to immediately take effect
The downside to the unchecked option is that members of the DL are bound to receive a lot of spam. In this case you’re better off with an Anti-Spam product to protect your environment.
