As organizations continue to migrate their local solutions to Cloud vendors, this often includes the migration of local email archives to a Microsoft 365. These email archives can consist of individual mail user archives, single instance journal archives or a combination of both. This blog posting will focus specifically around migrating a single instance journal archive to Microsoft 365. First, let me explain what a single instance journal archive is.
A journal archive is an email archive that consists of a single instance of every message that flows through an email server prior to be delivered to the users. This eliminates the need to archive from each user’s individual mailbox. If archiving for retention purposes were employed on a per user mailbox basis, there would be significant numbers of duplicate data. Each message, a copy would need to be created for each user listed in the To, From, CC and BCC fields. This would require massive amount of diskspace to accommodate all these duplicate emails. The purpose for the journal is to ensure that a single copy of every email is retained for legal purposes regardless of how many users are listed in the address fields or within distribution group. This process also ensures that an end user cannot delete a message before their mailbox is archived.
Within Microsoft 365, there is no such thing as one of these journal archive solutions. With Microsoft 365, each mailbox must contain only the data for the individual user named for that mailbox and not mail for any other user. This is called single custodian email accounts. When a journal message is migrated to Microsoft 365, a copy of that message must be placed into each intended recipients’ mailbox. This is the process of de-journaling the email; the single instance message must be replicated for each listed recipient, and the sender as well. Given that until we look at an individual source journal email to determine first its size and then the number of recipients, we have truly no idea of how big this message will become once replicated to all recipients.