Offline Address Books and their existence when running different versions of Exchange comes up alot. So wanted to post up this great article  that covers off what you need to know.

Before installing your first Exchange 2013 server during a migration project you must first review your offline address book configuration.

The issue, as explained in detail by Exchange MVP Andrew Higginbotham here, and mentioned by Microsoft in the release notes and a subsequent blog post, is that Exchange Server 2013 will create a new default offline address book for the organization.

Any mailbox users who do not have an existing OAB assigned to their mailbox directly, or to the mailbox database that they are located on, will download the entire OAB from the new default OAB that Exchange 2013 creates. In organizations with a large OAB or distributed network environment this is obviously not ideal.
Continue reading → Exchange Server 2010 to 2013 Migration – Reviewing Offline Address Book Configuration