Since the update 26 my mail app doesn’t download new mail.

Since the update 26 my mail app in my iPhone and iPad won’t download mail. I can send mail. I use optonline.net for mail. I tried all the “regular fixes”

but it still reads ”access denied “ “error” not responding verify you have the correct account information.. which I have done. Idk if the issue is from optonline.net, the app or the update.