Hello Jason
many thanks for you assistance with this. Using the commands above I have been able to change the email address of the old public folder and reassign it to a new online pubic folder.
However, on-premise users are not able to email the new folder as the address is not recognised. I have tried to run the Import-PublicFolderMailboxes.ps1 on-premise but it fails with "Unable to find type [PSCredential]: make sure that the assembly containing this type is loaded"
thanks
Frank.