When de-duplicating WITHIN custodians (vertical de-dupe), you are removing all duplicate items that an individual has in their mailbox, across different versions of their mailbox, as well as data contained on their workstation and/or user network share(s). For example, perhaps the custodian is on a mailing list and sends an email to the list; she will probably have a copy of the email in her Sent folder as well as in her Inbox from the mailing list. Similarly, if the user has multiple mailboxes (perhaps the user created an archive of her older messages), there are likely to be emails that exist in both places. When you de-duplicate ACROSS custodians (horizontal de-dupe), you remove all but one copy of an email or document from all the custodians.  For example, if a manager sends out a memo to her staff, that email will be in each staff member’s Inbox and in the manager’s Sent items folder. Horizontal de-duplication will remove all but one of these emails from the review database.

 

The main difference with these two options is the amount of data to process and review.  If you de-dupe WITHIN custodians, you will have duplicate items processed and in the database that will be reviewed.  If you de-dupe ACROSS the custodians, only distinctly unique documenst will be processed and loaded for review.  This will speed up the time for review and lessen the overall processing costs.  In the past, if a collection was de-duplicated ACORSS custodians, and you found a document in the review that was sent to Mr. Jones, it might not have been possible to tell if that document sent to Mr. Smith.  Now however, vendors, including Iris, can track this information so you can tell who else received the document. Similarly, if required, duplicative documents can be re-introduced into the collection at a later date for production purposes and be produced with their parent duplicate file.