some how I got knocked off the email alert list. I just saw that 6.5.2 has a fix:

Email Encryption Retry
IronPort AsyncOS for Email 6.5.2 offer enhancements to the email encryption workflow. Now,
outgoing messages that meet the encryption filter condition are placed in a queue on the
Email Security appliance for encryption processing. If a temporary condition exists that
prohibits the encryption of emails in the queue (i.e., temporary C-Series busyness or CRES
unavailability), messages are re-queued and retried at a later time. In the encryption profile,
you can configure an encryption failure notification message for users, which is similar to
message bounce notifications.