Use case: Use this procedure to configure sender authentication for a group or user mailbox. Enabling this setting wil only allow messages from people inside your organization to be received. Messages from external senders are automatically rejected, helping reduce spam and unauthorized mail flow.
To configure sender authentication, do the following:
- Open Group properties, select the Mail tab, and click Delivery Restrictions.
- To reject emails from external (non-authenticated) users, configure Accept messages from to include only trusted senders and reject all others.
- To allow emails from external users, deselect Require that all senders are authenticated.
- Configure Reject messages from to block messages from specific users while allowing others.
- Click OK twice to apply the settings.
You can apply the same configuration for users or mailboxes under the Mailbox tab → Delivery Restrictions.
ID:KB_026_HowToConfigureSenderAuthentication
