I’ve been using Mail on an instance of NC 13.0.1 for months. This week I updated the Mail app to 0.8.3 and it stopped connecting to the IMAP server where my email is hosted. I tried deleting my mail account and creating it again, didn’t work. I tried deleting the mail app from NC and reinstalling it, didn’t work. I tried connecting to a gmail account, doesn’t connect. I called my email provider who said that in their logs they don’t even show the app attempting to connect to their servers.
EDIT: Other mail clients and the email provider’s web app are working fine. It’s only NC Mail App that doesn’t want to connect.