The simplest way to determine the size of your Source Public Folders is to run a PowerShell query to obtain the size-related statistics from your Public Folders.
Here is an example script that will pipe the results into a file named PFStatistics.csv. You can then use this information to break up your Public Folders into smaller-sized Public Folders. Add up the total item size for all folders to determine the total approximate amount of data being migrated.
Get-PublicFolderStatistics | Select-Object Name, FolderPath, ItemCount, TotalItemSize | Export-csv .\PFStatistics.csv -NoTypeInformation
- If your Source is Exchange 2007, and any Public Folders contain more than 20,000 items, these should be broken into multiple Public Folders.
- If your Source is Exchange 2010 or later, and any Public Folders contain more than 100,000 items, these should be divided into multiple Public Folders.
- The Microsoft TechNet article here provides further detail on Microsoft Public Folder size limitations.