AJ,
As Stephan mentioned, the best way is to Quarantine the Email and then use your MTA to hold the email for an X number of days (Configurable in most MTA's). Once quarantined the email will need to be released and sent, based on someones approval.
SYMC Mail gateway has the integration done seamlessly, so the release aspect works through the DLP console. In order to do this with a different MTA, it would require someone to log into the MTA's console and manually release it OR build a custom Flex Response API that you can call from the DLP console. (I know that ProofPoint is building (about to release) an API process so someone can build this)
Hope this helps..
Good Luck,
Ronak
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