I have connected both iCloud, Yahoo Mail and an Archival V5 MBOX Mailboxes to Mac Mail. I am trying to migrate old emails iCloud to Yahoo Mail for its unlimited storage. However the when I tell a group of messages to move to the new Mail Box Mail.app acts like it is preparing for the move but the messages actually never get moved. It doesn't matter if I highlight them and select Move or Drag and Drop Them. This seems like a serious bug in Mail.app. Anyone have any ideas or workarounds? I am going to try AirMail in the meantime and their Message "Cloning" feature which can move emails between Mailboxes. I would have done the migration via Outlook and a PST file but the mail I need is in the Archival MBOX .emlx file type.