"Please open the Yahoo Mail app and sign in to use this functionality"

I was having the same issue recently. Prior to a couple of weeks ago I was able to send documents and photos, etc through Yahoo mail but recently that changed for an unknown reason. I deleted the app from my desktop then reinstalled it from the App Store and it is working again. I can now send photos and the like without having to see that statement, "Please open the Yahoo Mail app and sign in to use this functionality."

Hi, I had the same issue recently. The following resolved the issue: I deleted the Yahoo app without signing out of it and reinstalled it from the app store. After reinstall, my accounts and mail were still there (nothing changed). Now, I can upload photos without the "sign in to use this functionality" message. So, the reinstall fixed it.

Tried selecting a photo from iphone photo app then I selected the Yahoo Mail app to attach it. I received the message "Please open the Yahoo Mail app and sign in to use this functionality". I am signed into the Yahoo app. This has consistently worked for me until today. Any ideas? I see the Yahoo Mail app has been updated recently

Talk to Yahoo. It's their app.