Is it possible to mark external emails as internal by sender IP address?

Question

For the purpose of email delivery to distribution groups, is it possible to mark emails from an external sender as an internal email by sender IP address? We'd like distribution groups to receive emails from specific senders without setting the group to accept email from all senders. It looks like the X-MS-Exchange-Organization-AuthAs header cannot be modified so is there another method we could use?

Answer 1

Use a transport rule to drop messages from all external senders except the allowed ones. Set the Group to accept mal from all senders in including external, use the transport rule to protect it