This has nothing to do with Enterprise Vault, but exchange. 

Standard message-only journaling simply delivers a copy of a message flagged for archival to a designated journal mailbox. Envelope journaling instead delivers archival messages using an envelope message containing a journal report with the original message as an attachment.

Envelope Journaling is available in Exchange 2000 Service Pack 3 and Exchange 2003 Service Pack 1 and later. Exchange Envelope Journaling is used to capture all the available RFC2821 and RFC2822 recipients, including CC and BCC recipients that were configured on an email message. It also captures members of a distribution group expansion and it captures reports that include delivery receipts, NDRs, read receipts, and out-of-office notifications.

Envelope journaling enables you to archive the following information to specified journal mailboxes:

• All the recipients of the message (P1 data as contained in the Simple Mail Transfer Protocol (SMTP) conversation)
• Distribution group lists are completely expanded and included in the above list The journaled message consists of a multi-part Multipurpose Internet Mail Extensions (MIME) message with the following contents:
• Plain text that contains information about the complete list of P1 recipients, the recipients specified in the SMTP conversation by the RCPT TO: command, and original message ID.
• The original message as attachment

You can enable Envelope Journaling by using one of these methods:

1. Use the ADSI editor management console.
2. Use the Exchange Server Email Journaling Advanced Configuration (exejcfg.exe) tool.

So unless you using Exchange 5.5 or Exchange 2007, yes you do need to use one of the above methods. I will see if I can write an article on this sometime.