There is a o2m / m2o link between mail.message and mail.shortcode. However this link is not used: 'messages' (m2o from shortcode to message) is never set. Anyway there is no usage of this link: shortcodes are replaced in message body and that's it. Task-3557985 (Mail: Message cleanup (shortcode, link)) Prepares Task-36879 (Mail: Support MultiCompany Aliases) Part-of: odoo/odoo#138938