Error Message

Export out the Unprocessed Documents list of items to CSV and examine.

• Primary reason is usually CRAWLER_DROPPED_MSG.
• Description: EsaMapiSearchFolder: Invalid sent time or not set

This can be caused by a feature used with Shared Mailboxes.  Exchange will auto-generate a copy of the original message as a 'forward (Fw:)', so that a copy will be retained. The copy is intended to be retained in the Shared Mailbox's Sent Items folder.

These can be identified by a common prefix (Fw:) in the subject line of the message in the CSV. 
Example:

• Fw:'FW: Current Data Reports'
• Fw:'RE: Current Data Reports'

When the native file is opened the original email message is included as an attachment. The body content of the forward message is blank or may contain the generated 'forward' message:

"The attached message was sent by a member of this shared mailbox.  Usually, it would appear in Sent Items, but your service is currently being upgraded.  Things will go back to normal after the upgrade."

This is due to a certain Shared Mailbox flag [ MessageCopyForSentAsEnabled ] being enabled by the Exchange administrator.
Reference:  https://www.michev.info/Blog/Post/1947/messagecopy-settings-and-forwarding

The email is generated by Exchange.  Since it is an .msg file, Enterprise Vault will journal and archive it.
 

To verify the Exchange settings for [ MessageCopyForSentAsEnabled ] , open Powershell and enter the following command:
Get-mailbox | select messagecopyforsentasenabled.
→ If True, the setting is enabled

If the requestor is requiring these files, there are two options to provide the native file(s).

1. From the Exceptions > Unprocessed Documents tab.  Export the native files. (see 'Viewing Processing Exceptions in the Veritas Case Administration Guide) https://www.veritas.com/content/support/en_US/doc/Case_Administration_Guide_10.1)
   Or:
2. If the native files fail to export, export the list of documents to CSV.  The source (PST) location is identified in the CSV.  Obtain a copy of the PST.  Using Outlook, search for the item within the PST and extract the item to provide the native message to the requestor.

Note:  The original message was likely processed into the eDP Case.  Confirm in an Analysis & Review search.