Till now we were using only Webmail in Zimbra. Now some of our users wanted to use Outlook+POP3. While we were testing , I found one thing .

In new message window of outlook , users are able to insert the "From" tab and able to send from anyuser@anydomain.com.

For example: abc@mydomain.com is able to send mails from pqr@mydomain.com or pqr@adifferentdomain.com using outlook. It is delivered to the recipient, saying that abc@mydomain.com on behalf of pqr@mydomain.com.

Please tell me how can I block this from Zimbra.