An account configured with SMTP only (no imap_host) has no inbox, but the
inbox list path still called _imap_connect, which handed an empty host to
imaplib. imaplib.IMAP4("", 993) silently dials localhost:993 and fails with
"[Errno 111] Connection refused", so the email panel's poll logged a
"Failed to list emails" ERROR every ~60s and surfaced a scary error in the UI.
_imap_connect now fails fast with a typed EmailNotConfiguredError (subclass of
RuntimeError, so existing broad handlers keep working) when no imap_host is set,
and the inbox list returns an empty result for that case instead of an error.
SMTP send is unaffected.
Ricardo
3b4187e25d