Public user by default don't have email. So when you try to subscribe to a channel in public user (portal don't receive an email), the email cannot be send and the user see a message: "Unable to post message, please configure the sender's email address. closes odoo/odoo#60867 X-original-commit: 7e40af524cc1b23abab3140377d993f3e93c5cf0 Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>