'Override to get the reply_to of the parent project.'

@api.model
def message_get_reply_to(self, res_ids, default=None):

    issues = self.browse(res_ids)
    project_ids = set(issues.mapped('project_id').ids)
    aliases = self.env['project.project'].message_get_reply_to(list(project_ids), default=default)
    return dict(((issue.id, aliases.get(((issue.project_id and issue.project_id.id) or 0), False)) for issue in issues))
