Yahoo email on my iPhone 6 will not update server.

SImply put, when I check my yahoo mail from my phone it will not update as a read message. This is also the case for my "mark all messages as read." It will work while in the app (e.g., it functions as normal), but when you close it and open back any changes you made come right back (read messages, deletions, etc). I have deleted my profile and added it back along with several resets. Any help is greatly appreciated!