I ran into this bug using bzr_hookless_email, fortunately someone had published a patch which seems to have fixed the issue:
=== modified file 'bzr_hookless_email.py' --- bzr_hookless_email.py 2012-03-22 15:15:15 +0000 +++ bzr_hookless_email.py 2012-04-25 06:05:55 +0000 @@ -159,7 +159,7 @@ self._config = self._branch.get_config() def update(self): - smtp = SMTPConnection(self._config) + smtp = SMTPConnection(self._branch.get_config_stack()) smtp_from = None for revision in self._revisions_to_send(): msg = self._compose_email(revision)