Google Message Encryption Administration Guide - Manual (Page 27)

28 Postini Encryption Services Administration Guide
If the message expires without being read, the sender will receive a notice.
If the recipient replies to a message, Portal Delivery sends the reply back to the
email protection service, which routes the message to your inbox. Replies are
filtered by the email protection service using the same protection as any other
inbound messages.
Filtering
Before a message is routed to Message Encryption, the email security service
applies the same filter rules as all outbound mail.
The Email Security Service filters all mail before sending it to the portal. All
Attachment Manager or Virus filters still apply.
Content Manager rules with a disposition of “Message Encryption” override any
other Content Manager disposition except “Log and Deliver.” Content Manager
filters may not apply if you use a Message Encryption rule in Content Manager.
Note: If an outbound message is quarantined, then released from quarantine, it
will be sent through normal mail delivery, not Message Encryption.