Simplifying Email Backup with MAPI

Simplifying Email Backup with MAPI

Email message are at the top of the list of the kind of data users wish to backup and protect. Yet these messages are also one of the more difficult types of data to backup. Let’s look at the challenges in backing up this type of data and then discuss how inSync does it.

 Microsoft Outlook is one of the most widely used email clients. Outlook stores email messages in files known as PST files. Most of us have PST files that are a few GB in size, and it isn’t uncommon for them to be in the tens of GB. Traditional backup software, which simply identifies and stores these files, has the following limitations:

  • Slow, resource-intensive backups: Before an incremental backup, any changes in our email since the last backup have to be identified. Because Outlook stores our messages in big PST files, it takes a lot of resources to identify any changes.
  • Poor deduplication accuracy: Small changes, like the arrival of a new email message, lead to multiple changes in a PST file. This creates more data that must be backed up, leading to bigger backups.
  • Locked file issues: Outlook prevents other applications from accessing PST files while it runs, which is problematic since most of us usually leave Outlook running.

inSync differs from traditional enterprise backup software because it deals with individual email messages, rather than PST files. It relies on Messaging Application Programming Interface (MAPI) and queries specific attributes of messages in mailbox. These attributes are compared with a local reference and any new or changed messages are identified. New messages are backed up, as well as any attachments.

The use of MAPI gives inSync a number of advantages:

  • Querying email messages directly instead of large PST files results in faster and smaller backups.
  • Using global deduplication means inSync backs up only a single copy of a message that may appear in the mailboxes of multiple users.
  • Deduplicating email attachments as well as messages means that if an attachment is the same as a file in a folder outside of email, only a single copy is saved.
  • Restoring email data is easier for the user, because they can restore only the folder they need instead of an entire PST file.
  • Accessing email messages directly avoids the issue of being unable to access locked PST files and creates more consistent backups.

Beyond improving the backup process for email messages, this type of approach could make other email-related improvements possible. These could include the ability to restore individual messages, as well as e-Discovery capabilities for insight into message content. By making email data more manageable, MAPI offers possibilities for how that data can be used.

Anand Apte

Anand Apte

Anand has over 12 years of experience in product development. He has been with Druva team from early days, and works as a lead engineer for inSync. Prior to joining Druva, Anand worked as a file system engineer at Veritas Software.


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