The issue occurs because the Exchange Server already resolved the messages to their corresponding Active Directory accounts, since these messages are from an internal sender and sent to an internal recipient.

To make the exception work, type the user account name instead of SMTP email address. For example, if you want to add domain.user@domain.com, you should also add "Domain User" in the exemption address list.

1. Log on to the WFBS console.
2. Click Security Settings.
3. Under My Company, select the Exchange Server and click Configure.
4. Click Content Filtering.
5. Click Add and select Create an exception list for email account(s).
6. Click Next.
7. On the Rule Name field, type a rule name. For example: Exceptions.
8. Under "Specify an email account list exception rule:", add the Domain User Account and click Finish.
9. On the Content Filtering page, tick the Exceptions Rule check box and click Reorder.
10. Set a higher priority for the exceptions you just created to bypass the other rules beneath it.
11. Click Save Reorder.
12. Click Save and then close the WFBS console.