Ever wanted to check which documents Exchange Search couldn’t index? The Get-FailedContentIndexDocuments cmdlet gives you exactly this information: it will return a list of documents that couldn't be indexed including an error code and the reason for failure.
The most common cause for this is the lack of an available filter for that document type. For example, if the PDF filter is not available (which is not by default) and if an e-mail contains a PDF document, the document is marked as failed content indexing as Exchange can’t index it.
After a new filter is installed, only new messages with attachments of the type for which the filter is installed are indexed. If you want to index older messages for that document type, the mailbox has to be moved, which triggers Exchange to re-index the whole mailbox content.
Some examples of reasons for failure are:
• “The document format is not recognised by the filter”;
• “This is an encrypted document”;
• “Filter not found”.
To retrieve a list of items that couldn't be indexed by Exchange Search from the mailbox of user Nuno:
To retrieve a list of items that couldn't be indexed by Exchange Search from the mailbox database DB01:
Get-FailedContentIndexDocuments -MailboxDatabase DB01
Hope this helps!