You are a messaging professional. Your company uses a Microsoft Exchange Server 2007 messaging system.

The company has two offices. Each office is configured as a Microsoft Active Directory site. Exchange Server 2007 computers are deployed on each site.

The company deploys an Edge Transport server in each office. All Internet e-mail messages are sent through the Edge Transport servers. Custom SMTP connectors are configured on each Edge Transport server.

The companys security policy states that no messages that contain client account numbers can be sent through the Internet. Users must be able to send these messages to other users inside the organization.

You implement an Edge Transport rule on one of the Edge Transport servers that prevent users from sending messages that contain client account numbers through the Internet.

A routine audit identifies that messages that contain client account numbers are still being sent through the Internet.

You need to prevent users from sending e-mail messages that contain client account numbers through the Internet. You also need to ensure that all other message delivery systems remain unaffected.

What should you do to prevent users from sending e-mail messages that contain client account numbers through the Internet?