Hi Jdsouza,
DLP Email Prevent will "modify the Email Header" with ANY term or phrase "encrypt". This will then be recognized by the next hop MTA which will then route it to the Email Encryption Server.
The MTA will route the email to the encryption server for it has a RULE. To route all emails that contain "encrypt" in the header to the Encryption server.
This is how MTA's work. It is also very seamless and most people who already have an Encryption server do things. So it is the least intrusive approach to integrating the DLP servers.