Microsoft Exchange is an e-mail program that will allow you to block outgoing e-mails. Some workplaces opt to configure the delivery restriction of the email service to ensure their employees aren't engaging in e-mail activity unrelated to work, and blocking outgoing e-mail is one way to ensure this. The email settings can be configured to block outgoing e-mails to the preference of the user, for example, allowing internal e-mails but not permitting external e-mails.
Click "Start" and select "Exchange Management Console" from the Start menu.
Click "Recipient Configuration."
Click "Properties" under the recipient that you want to configure the restriction for.
Click "Mail Flow Settings" tab and select "Message Delivery Restrictions" from the list.
Click "Properties." You will see several options.
Check the box for "Require That All Senders Are Authenticated" if you want to reject messages from external senders.
Check the box for "Only Senders in the Following List" if you want to specify which outgoing e-mail addresses can be received.
Check the box for "No Senders" which will not reject any outgoing e-mails.
Check the Box for "Senders in the Following List," which will prevent the recipient from receiving e-mails from the senders specified.