msExchRequireAuthToSendTo

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Restrict a Distribution List to internal users only

Restrict a Distribution List to internal users only

For restricting Distribution list to internal users only we need to set that attribute msExchRequireAuthToSendTo to TRUE in your on-premise AD environment and wait for DirSync to run.

This will make the DL in the Administration Center to untick the ‘allow external senders’ box on the DL’s and prevent any external senders from sending to those distribution lists.… Read the rest