A Dtrace of the JournalTask will show the following:
The Journal Mail Items have been modified, this has been seen with Symantec Mail Security for Exchange, where the original message that is attached in the Journal Envelope message is replaced with a plain text file named 'Quarantined Attachment.txt'. When Enterprise Vault encounters such an item the Journal Archiving agent sees the Journal Mail item as a normal well formed Envelope message, however the text file attachment does not conform to a standard Envelope message.
Workaround
The program that has modified the problem messages should be reconfigured to not replace the attached original message with a text file. If Mail Security for Exchange is identified as the program that has modified the messages there is a configuration document:
This issue has been addressed in the following releases:
Enterprise Vault 11.0.1 Cumulative Hotfix 1 Release
https://www.veritas.com/docs/000024613
Enterprise Vault 12
The following link contains information about Enterprise Vault 12
https://www.veritas.com/docs/000099905
Note: For information on how to obtain Enterprise Vault 12 see: How to obtain the license key and installation download for Veritas products