Exchange script: Fix broken migrated email addresses by splicing the historical LEDN in as a new X500 address

1/7/2018: I was working on a mail migration and needed to dust off and use this script, so I figured I'd go ahead and post it.

The underlying purpose for this script is, to workaround and suppress...
    # 550 5.1.1 RESOLVER.ADR.ExRecipNotFound; Not found'
... errors for users replying to email that has been migrated from an external mail system.