Answer for Why are we seeing a "MIGRATED Junk E-Mail" folder after the migration completes?

This is by design…here’s an explanation.
 
Outlook, in this regard, is not very smart.  The first time Outlook opens to a newly migrated mailbox, it looks to see if the standard folders exist (Calendar, Contacts, etc.)  The Junk E-Mail folder is one of Outlook’s standard folders (but not necessarily Exchange’s). 
However, if Outlook finds a Junk E-Mail folder it also assumes that the rules related to the folder also exist – it does not check to see if the rules actually exist.  As such, if the folder was created during the migration called Junk E-Mail (English version – convert to your language specific version), Outlook would not create the rules for it – essentially breaking the folder. 
From a product standpoint, we didn’t want to leave the junk folder’s data behind, and we didn’t want to break its functionality in the target mailbox, so the folder is prefixed with the word “MIGRATED”.  The folder is just a simple folder that a user can delete after the migration, move, rename, or whatever.
There is only one option related to this and it is a registry override to control the text of the prefix.  So, if you wanted the prefix to be the Dutch word for “Migrated”, you could specify such…but there’s no way to suppress the behavior.  In addition, for those who will try to be clever, setting the registry value to an empty value will cause the migration to fail; setting the value to match the source will break the folder.

Here’s the registry setting that can control the prefix:

The value above uses a pattern where the token ‘{foldername}’ is replaced with the current folder’s actual name.  Text can be placed on either side of the token, or only on one side.  Placing forward ‘/’ or backward ‘\’ slashes in the name are treated as text and will become part of the folder name; they are not seen as folder path delimiters.
Priasoft provides no support beyond the recommendation to have a prefix or suffix on the name.