If it keeps reappearing and the Mail Dispatcher Agent still crashes, you need to do one more thing in akonadiconsole. Go to the Browser tab, find the outbox you want to use, right click on it, Folder Properties, Attributes tab, enter SpecialCollectionAttribute then Add, double click on the Value near the SpecialCollectionAttribute and enter outbox. Add also another attribute, the attribute name has to be ENTITYDISPLAY and the value ("outbox" "mail-folder-outbox" "" ()) (just copy paste from here). Restart akonadi and now you should be able to remove completely the unneeded local folder account.
