Best Practices for Public Folder Preparation before Migration

Before starting any type of migration, you need to setup the infrastructure and prepare for the migration. Migrating mailboxes from on-premises Exchange Server to Exchange Online is a manageable process. However, migrating public folders is a little bit more complicated as there are several tasks that need to be performed. So, it is important to do some preparation before migrating public folders. In this article, we will mention some best practices (for public folder preparation) that you can follow when migrating public folders from Exchange Server 2010, 2013, 2016 and 2019 to Exchange Online.

An Overview of the Public Folder Migration Process

The process of migrating public folders is divided into three parts. We will go through each part in the best way possible to prevent any mishaps during migration or any loss of data.

There is no command to migrate public folders. For this, you need a series of PowerShell scripts to perform the migration. These scripts can be downloaded from the below links.

• For Exchange Server 2010 (Link to scripts)
• For Exchange Server 2013, 2016, and 2019 (Link to scripts)

The preparation work is an important part of the migration process. It’s fundamental for a healthy and smooth migration process. There is a lot of work involved in this process. If you follow the process, you will surely face minimal disruption or issues.

Here are some things you need to consider when migrating public folders to Exchange Online.

• When migrating to Exchange Online, there is a limit of 250,000 public folders.
• Once the migration batch is complete, no more data from the source can be copied over to the online counterpart, if not manually.
• You cannot be selective in the migration process.

Cleaning up

The first thing is to find out which public folders are to be migrated. If there are public folders, which are not needed anymore, you need to export and remove them from the setup as there is no granular migration and the migration batch will migrate all the configured public folders. You can also opt to migrate some of the public folders to Office 365 Groups but this needs to be done beforehand.

You can use the below scripts to identify the public folders which are not used anymore or have not been used since a particular year.

For Exchange Server 2010

$date=(Get-date).AddMonths(-24)
Get-PublicFolderStatistics -ResultSize unlimited | ?{$_.LastUserAccessTime -le $date}        

For Exchange Server 2013 and later versions

$date=(Get-date).AddMonths(-24)
Get-PublicFolderStatistics -ResultSize unlimited | ?{$_.LastModificationTime -le $date}        

Once this is done, the next step is to do a clean-up process to remove old or irrelevant data. This would involve the business and all the users which use the public folders.

Public Folder Size and Item Sizes

You need to check the size of the public folders and items to ensure they are not too large. If there are any large items, then you need to either remove them from the public folder and store them somewhere else or delete them. You need to remember that you will only be allowed to create one migration batch, which means that all public folders will be migrated in a single batch run.

Each public folder size must be between 15 GB and 25 GB. If these are larger, then they must be split into multiple smaller public folders. If you want to migrate large public folders to Exchange Server Online, then you need to increase the limit.

You can use the below command to identify the objects which are larger than the limit.

$pf=Get-PublicFolder \ -Recurse -ResultSize unlimited;foreach ($i in $pf) {$s=Get-PublicFolderItemStatistics $i.EntryID;foreach ($r in $s) {if ($r -gt "38600") {$r.MessageSize,$r.PublicFolderName}}}        

You can use the .\ModernPublicFolderToMailboxMapGenerator.ps1 script file to know how many public folder mailboxes are needed for the Exchange Online tenant.

The Mapping File

The Mailbox Replication Service (MRS) is the mapping of the local public folders with the Exchange Online counterpart. Here are some guidelines to follow on this.

• Ensure that the primary hierarchy is mapped to the root, i.e., “\”.
• Once an entry is added to the file, all subfolders will be migrated. There is no need to map the sub-folders.
• Double check the file to ensure the correct names are in it and there are no typos. ?

Excluding the Deleted Items

It is always suggested that you should not migrate the deleted items. If the dumpster is corrupted, this will halt the migration. You don’t have to go through each deleted item and empty it. You can just add the Exclude Dumpster in the migration batch script (see the below example).

New-MigrationBatch -Name PublicFolderMigration -CSVData <mapping file> -SourceEndpoint $PfEndpoint.Identity -SourcePfPrimaryMailboxGuid <GUID> -ExcludeDumpsters        

Connectivity

The connectivity testing is important to ensure that nothing is being blocked between the local server and Exchange Online. You also need to consider that there is enough bandwidth. The connection must also be a reliable one as timeouts or high pings can lead to migration issues.

There should be a clear passage between the local server and Exchange Online. For this, you can check with the network team. Alternatively, you can use the Microsoft Remote Connectivity Analyzer to test the connectivity.

Conclusion

You may face issues while using the native tools for migration. You need to factor in the scripting and skilled resources that are required. Another important thing is that if the Exchange Server is not running and you have an orphaned database, you will not be able to migrate it. In such situations, you can use a third-party application, like Stellar Converter for EDB that can help you migrate public folders from local Exchange Server to the cloud (Exchange Online). With this application, you can open multiple databases with no size limit. You can browse through them and granularly export the data to PST and other file formats. You can also export directly to Office 365 and a live Exchange Server database. You can export user mailboxes, user archives, shared mailboxes, disabled mailboxes, and public folders.