Block Users from Sending Email

How to Block Users from Sending Email Outside your Exchange Organisation

We can configure Exchange to prevent users from sending mail to the Internet (and receive mails). The user can only receive e-mail from other Exchange users in the same organization. To set this, follow the following steps:

1. Create a new distribution group (mail-enabled) in Exchange.
2. Add all the users which are not allowed to send mail outside your organisation.
3. Modify (properties) the SMTP connector(s) that are used to send to the internet
4. Under the Delivery Restrictions tab, REJECT MESSAGES FROM, add the distribution group.
5. Start Registry Editor (Regedt32.exe).
6. Locate and click the following registry key:
   HKEY_LOCAL_MACHINE/System/CurrentControlSet/Services/Resvc/Parameters/
7. On the Edit menu, click Add Value, and then add the following registry value:
   Value Name: CheckConnectorRestrictions
   Data Type: REG_DWORD
   Radix: Hexadecimal
   Value: 1
8. Quit Registry Editor.
9. Restart the Microsoft Exchange Routing Engine service and the Simple Mail Transfer Protocol (SMTP) services for this change to take effect.