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The must-know Exchange public folder migration feature

If you run Exchange 2007 or 2010 and are moving to Office 365, the public folder batch migration feature will ease the process.

Public folder batch migrations mean an easier migration off of on-premises Exchange.

If your organization uses public folders in an on-premises Exchange 2007 or Exchange 2010 deployment, and you're considering a move to Office 365, learn about the public folder batch migration feature released in the recent Exchange 2007 Service Pack 3 Rollup Update 15 and Exchange 2010 Service Pack 3 Rollup Update 8 releases.

The idea behind these public folder migrations is to improve the throughput of the overall public folder migration process.  

Get ready for a public folder migration

Don't underestimate the preparation required to perform public folder batch migrations.

Review Microsoft's documentation on this process to learn about specific requirements as well as any new information regarding the process. This guidance will help you create an overall migration plan, but the Exchange Online Service Description will explain the constraints of a public folder deployment in Exchange Online. Other areas to review include the permissions required to perform the migration, the quantity and sizes of the current on-premises public folders and enabling Outlook Anywhere within the on-premises Exchange infrastructure.

Before migrating all on-premises public folders to Office 365, perform an inventory of your public folders and their content, which could reveal unwanted, removable items. This inventory may lessen your remediation work and possibly speed up the migration.

The overall migration process involves running many PowerShell commands and scripts. Exchange Management Shell commands run against the on-premises Exchange Servers to determine key remediation tasks; this includes detecting if any on-premises public folders have the backslash character in their names and renaming them. You may need to communicate any public folder name changes to end users before the change takes place. Other commands are available to export key public folder information, such as permissions, overall folder structure and general folder statistics, before the migration.

Your IT team can compare all of this information to the public folders' status after the migration, which is useful if there are any perceived discrepancies. There are also PowerShell commands that run against the Exchange Online deployment, both as preparatory tasks and ones to actually commence the migration. Assign the correct permissions within Exchange Online to run these commands.

Scripts assist you in a public folder migration

In addition to individual PowerShell commands, the public folder batch migration process uses a number of scripts available from the Microsoft download site. These scripts must run against the on-premises Exchange Servers to produce key output information, such as mapping files, and also to synchronize mail-enabled public folders to Exchange Online. Watch out for areas that may affect script operation and the actual migration, including the source public folders' size and the maximum size of Exchange Online public folder mailboxes.

Microsoft's specific guidance for these areas, including appropriate mitigation strategies, is included in its documentation on the process. If any single public folder exceeds 2 GB, for example, it isn't added to the output file of the script that calculates the number of public folder mailboxes to create in Exchange Online. Appropriate remediation action must be taken in the case, including splitting a single public folder into multiple public folders, removing public folder content to reduce overall folder size or manually adding the affected public folder to the output file -- as long as that folder doesn't exceed 30 GB.

Another aspect of public folder batch migrations to Exchange Online is detecting previous public folder deployments or migrations in Exchange Online. In this scenario, determine whether any public folder mailboxes, public folders or public folder migration requests already exist within the Exchange Online environment, because these can affect the batch migrations. Use Microsoft guidance's on which commands find and remove migration requests, public folders and public folder mailboxes in Exchange Online. If any of this information is detected in Exchange Online, organizations may benefit from understanding who created this content and why.

Now you can create public folder mailboxes in Exchange Online and synchronize the on-premises, mail-enabled public folders to Exchange Online via Microsoft's recommended scripts. You must obtain any information from the source Exchange environment to create the migration batches, such as the LegacyExchangeDN of a mailbox server hosting a public folder database, or the Outlook Anywhere server's fully qualified domain name.

Consider downtime and rollback in a public folder migration

Budget for public folder downtime to complete the migration in your overall project plan. Downtime ensures that end users can't access the public folders and that the migration cutover can complete successfully.

A rollback is made possible by reactivating legacy on-premises public folders, but any posts made to the public folders that migrated to Exchange Online, or any email sent to mail-enabled public folders migrated to Exchange Online, won't migrate back to the on-premises public folders. In these cases, you'll need to manually export and import the affected content via a PST file.

About the author:
Neil Hobson is a U.K.-based Microsoft consultant with a background in the design, implementation and support of infrastructure systems covering Active Directory, Windows Server, Exchange and Lync. He is currently focused on Office 365 in technologies such as Exchange Online, Lync Online, SharePoint Online, Yammer and Office ProPlus. He is also focused on the associated areas of identity, networking, migration and service integration. Neil is a member of the Chartered Institute for IT (MBCS) and was also a Microsoft MVP for Exchange Server from 2003 to 2010.

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This was last published in July 2015

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