This commit renames some internal mail.thread methods linked to the notification process. This is the next commit of a series aiming at improving code readability and method finding through prefixes. See notablycae1c3977f,cdfe479e2eandfc1348dd3d. This commit does not change any functional feature. It does only rename notification-related methods, using the _notify prefix to ensure they are private and to mark they are part of the notification process.