Mail app IMAP accounts got messed up after upgrade to Sierra completed (from Mavericks). One IMAP account got completely lost, e-mail messages saved to privat and local message boxes are saved. Few other messes in accounts definitions more. Is it possible to import manually accounts definitions from Mavericks where everything was fine? Mavericks backups are available, Time Machine and of other kinds. Generally all e-mail messages are kept in local and private mailboxes without any connections to servers. In rare case these are left short term stored on servers.