We have the option to sync from stock messaging, but not to stock messaging. The reason for this is for people like me that don't have all of the messages in the stock messenger because we've used textra for a while and titanium backup to restore our textra messages for a while, but are now moving to a different, unrooted phone. This way, we could sync all of our messages to the stock messenger then use a third party app to actually back the messages up.