When somebody sends an email to a community, the sender is the email address. If that person is an external user, the sender address is the external email address.
When that external user sends a mail to other external members in the community. The mail servers reject that mail, because it looks like mail relay.
We would like to have the ability to change the sender address to a default configurable address ("NoReply" or "CommunityAdmin") for external users so we don't have the mail relay issue.
External User1 : user@BBB.com
External User2: user@CCC.com