[Zope] securityinfo for a class

Hello, I'm creating a Product with a function retrieve(self, num) which returns an email.Message object. In a zpt of the product I've <div tal:define="msg python:here.retrieve(request['num'])"> and I would like to manipulate msg using email.Message methods, like in <td tal:content="python:msg.get('from')">name</td> I've added these delarations to my __init__.py ModuleSecurityInfo('email').declarePublic('Message') ModuleSecurityInfo('Message').declarePublic('get') This doesn't work, it prompts the login box. How can I use Message's methods in a page template or Python Script? Fernando