Exchange 2010 Cross-Forest (Cross-org) Client Migration Planning

After some absence, I’ve decided to get my blog running. I have a couple of ideas of what I would like to publish but that will have to wait for now. This week I’m performing a cross-forest migration for a client. After reviewing the assistance available for CLIENT – SIDE CONSIDERATIONS on the Internet, I thought I’d start publishing a list of issues I have encountered so far. It would be great if you could leave your comments so that I can update the list so that it captures a well-rounded list of scenarios and possible issues.

This is a WORK IN PROGRESS – Feel free to send me your comments.

This client has two active directory forests. Both forests have a mix of Windows 2003 and Windows 2008 R2 servers as DCs. The legacy Exchange organization has Exchange 2003 deployed, while the target organization has Exchange 2010 SP1 deployed. The client active directory accounts have already been migrated but are still accessing their mailboxes in the legacy forest / organization. The user accounts used to access the existing Exchange 2003 organization are still the old accounts in the legacy forest.

The Outlook clients deployed in this scenario are:

• Outlook 2003
• Outlook 2007

Here are the items I need to review:

• Outlook client versions.

If Outlook 2003 is in use, either change the encryption requirements on the CAS server or change the Outlook 2003 client to require encryption when connecting to Exchange 2010. See Outlook  connection issues with Exchange 2010 mailboxes because of the RPC encryption requirement for more information.

• .PST files (archive.pst, <mailbox>.pst..all stored locally)
• Boss / Admin relationships / permissions
• Shared mailboxes
• Calendars
• Resource owners – Conference rooms, etc.
• Locally stored Outlook rules

Fortunately, the client is having Microsoft SCCM installed as we speak and are willing to upgrade all existing Outlook 2003 clients to 2007. The major question is this:

Can a mail migration be performed with minimal impact to clients?

It depends…If native Microsoft tools are to be used, you’re going to experience some disruption. Once the mailboxes have been migrated, a new Outlook profile will be required to access Exchange 2010 in the new forest. What does this mean for the user? All of the following will be “lost”:

• All configured .PST files. The existing Outlook 2007 users will lose their .OST file if they are using cache mode. A new one will be generated once the profile is changed to point to the new Exchange 2010 infrastructure and the client is still configured for cache mode.
• Local client side Outlook Rules will be lost and will need to be recreated.

The client is considering using Quest’s Migration Manager for Exchange. What will this gain over Microsoft tools?

• Mailboxes can be synchronized to the new infrastructure without being migrated. i.e. The day of migration will require a delta synchronize and cut-over to the new mailbox.
• Migration manager has an Outlook Profile Migrator built into the product. (Maintain the PST and OST settings)
• Public folders can be replicated in both directions.

NOTE: This article is a WORK IN PROGRESS. I will update this as more is uncovered.

August 1, 2011 - Posted by ivorb | Exchange 2010 RTM, Exchange 2010 SP1