Problem
When the user tries to send a large message of more than 10MB the Cisco IronPort Email Security Appliance is unable to encrypt the message and it becomes unresponsive. The user has to powercycle the IronPort to make it active again. Why does this happen and is there a way to adjust the maximum message size that the IronPort device can decrypt without any issues?
Resolution
Starting with the Cisco IronPort AsyncOS for Email Security Appliance version 7.6, the message size limit has been changed to 10MB as the previous message size limit of 40MB was causing too many issues like the encryption engine getting locked. So the message size limit was has been reduced from 40MB to 10 MB. For the 10MB size limit about 20% of the size needs to be accounted for MIME inflation and hence the actual message size limit is really about 8MB for the messages to be encrypted properly by the IronPort device and the user to send successful message.
Source:https://supportforums.cisco.com/thread/2142643?tstart=0
