Recently I completed a legacy Public Folder migration from Exchange 2007 to 2013. There was one thing that made the entire process painful….aliases.
The migration will fail during the Initial Seeding if a public folder is encountered with invalid characters in the alias. I encountered 3000 invalid aliases in 5000 public folders. It seems to be very common with public folders that were created in older versions of Exchange (2007 and backwards).
The link below shows a great way to determine these public folders. In addition, it helps correct their aliases if they have a space. However, the commands can be repurposed for other invalid characters (I had aliases with < and > in them):
https://justaucguy.wordpress.com/2013/08/22/troubleshooting-a-public-folder-migration-to-2013/
I recommend trying to scope out this work before a PF migration, and I will be sure to do so in any I run going forward.
