Hi,

I have enabled "Require that all Sender are authenticated" for a DG group to restrict external email coming to this address but it is not working.

I have tested this with different DG and have same issue.

Also when I restrict the DG to accept email from specified users in our domain it works fine internalyy and block it for usrs which are not in the list but still accept email from external domain.

Does this have anything to do with "Receiver connectors"?

I believe it does have something to do with your receive connector.  On the "Authentication" tab, if you have "Externally Secured" checked this will allow external emails to be sent to the DG.

Definition from the Help for that setting:

"When you select this option, you make an assertion of external security that
cannot be programmatically verified by Exchange Server"

Hi Vala,

Thank you for your question.

Did you create a new distribution group to check if the issue persist?

Did this distribution group migrate from Exchange 2007 or former?

In previous versions of Exchange, by default, no recipients were configured to require all senders to be authenticated. Therefore, any distribution groups that we migrate from a previous version of Exchange won't have this restriction configured.

We could refer to the following link:

https://technet.microsoft.com/en-us/library/bb124405%28v=exchg.141%29.aspx

Please tell us what is your transport rule? Including detail steps:

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim,

I created new DG and it worked as it was expected. I am new at my company but I know thy migrated from 2003 to 2010 and skipped 2007.

Do you know how can I fix this issue??