If I go to the home page of my NOCC installation (not having logged in yet) and simply click on the "Submit" button without typing anything at all in the Username: or Password: fields, I get an error message that isn't very user friendly:
Could not connect to server: IMAP Authentication cancelled
Surely that should say "No username supplied, please try again" or something like that. Also, at the top of the page, it shows you logged in as no-one (i.e. @mail.domain.name !!) complete with Preferences and Logout links. Not good. Similar things also happen if you type in just a username and no password at all (or the wrong password) - it displays an unfriendly error:
Could not connect to server: Can not authenticate to IMAP server: AUTHENTICATE LOGIN failed
when "Username or password incorrect, please try again" would be better, plus you're again given the impression at the top of the page that you're logged in (user@mail_domain is shown, again with Preferences and Logout links. The fixes needed are better error messages for novice users and not indicating you're logged in until you actually are.
Confirmed and in work...