How to Block Outbound Email to Untrustworthy Domains or E-mail Address for specific people ?

namlovely2011 

Here's how to do it in Microsoft Exchange Server:

1. Open the Exchange Admin Center.
2. Go to Mail Flow > Rules.
3. Click the plus sign (+) and select Create a new rule.
4. Give the rule a name.
5. In the Apply this rule if... section, select The sender is a member of... and choose the user or group you want to block.
6. In the Do the following... section, select Reject the message with the explanation... and enter a custom message explaining why the message was rejected.
7. Click More options.
8. In the Except if... section, select The recipient domain is... and enter the domain you want to block the user from sending emails to.
9. Click Save to create the rule.

This rule will reject any outbound emails from the specified user or group to the specified domain, and provide a custom rejection message.