If you are unable to accept or send new email on iPhone inhabitant Mail app, try installing Yahoo Mail app from Apple Store. Yahoo Mail not working on iPhone models. If nothing else work, the best treatment is to delete your Yahoo account from the Mail app and the iPhone and then add it back in. If you’re concerned about after any email, there’s good news! Your Yahoo email is always stored on Yahoo’s servers, so when you delete the account from your iPhone, you are NOT deleting any email.