You have an Exchange organization named contoso.com. All servers in the organization
have Exchange Server 2010 SP1 installed. The organization contains a mail-enabled
domain local group name Group1.
Users from outside the organization report that all email messages sent to
group1@contoso.com generate a non-delivery report (NDR).
You need to ensure that users from outside the organization can successfully send email to
group1@contoso.com.
What should you modify for Group1?

A.
The advanced settings.

B.
The mail flow settings.

C.
The group scope.

D.
The group type.

Explanation:
By default the Message Delivery Restrictions, under the Mailflow options, are set to require
that all senders to group mailboxes are authenticated locally by the server. This is not
acceptable if the group will be accepting mail from external domains, so the following
checkbox should be un-ticked: