After a successful migration of mail enabled public folders, it is observed that the "Send As" permission has not been copied and applied on any of the target folders. However, all other permissions appear to have been copied and applied.
While mail migration will apply the "Send As" permission for mailbox accounts, Public Folder Agents will not transfer this permission. Currently the Public Folder Agents will only copy the following folder permissions:
Currently there is no resolution to this known defect; to work around the issue - the "Send As" permission will have to be manually applied on the mail enabled Target Public Folders.
This article is still accurate. DEC 2015