iMessage Caution/Warning v5.1.2
If you have OS X EL Capitan, -Be Careful. It will Wipe your entire iMessage History completely Clean, even the folder that stores them. Make sure you have some kind of backup just in case. I hope they will fix this in a future update. I had to do a Time Machine backup on (iMessage Archive Folder) to get all my messages back but have NO idea how to transfer them back to the iMessage App.
UPDATE Mon, Jan.18 2016 : Corrected the problem of transferring the messages back to iMessage app by using Time Machine to Restore subfolder of “messages” and “containers/com.apple.ichat note, you must do the backup before you did the wash or it will not work.
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MacCleanse