Today I have been migrating Public Folders (yuk!) from Exchange 2010 to Exchange Online, and have come across a slightly odd issue.
I had followed the lovely guide to Public Folder migrations provided by Microsoft here, however I could not complete my migration as the migration batch had completed with errors. The error I was receiving was as follows:
Error: MigrationMRSPermanentException: Error: There are 2 mail public folder(s) in Active Directory that were not linked to any public folder during migration.
The Public Folders referenced in the error message were both Exchange system folders, so I wasn’t sure why it was bothering to try and synchronise them. Luckily the error message does give us a clue as to what to do;
You may also run "Set-MailPublicFolder -IgnoreMissingFolderLink:$true" for each AD object that is a legacy system folder and resume the migration
Being the silly person I am, I assumed that this command needed to be run against the legacy Public Folders On Premise, but apparently -IgnoreMissingFolderLink is not a parameter in Exchange 2010. What I actually needed to do, which is not obvious from the error message, was to run this command in Exchange Online. I ended up using a catch all command, which looked like this:
Get-MailPublicFolder | Set-MailPublicFolder -IgnoreMissingFolderLink:$true
Once this was done, I stopped the migration batch, and then started it again. It then performed it’s initial sync and I was able to continue the migration!