Em…… There was no such setting when I posted this but a few hours ago my email client suddenly became able to download all the emails again. I then enabled app password and the client no longer complains when I tried to add the account. However I find that the the email forwarding setting has disappeared from the WebUI and I can no longer turn it off. Also, when I tried to send to my z.org email from iCloud, I was told "The following organization rejected your message: haraka.elektrine.com." I haven't got any email on this account since 2 days ago. I think the recent upgrades to z.org must contain some large breaking changes and the my emails won't be available for a few days.