Impacted versions:

8.0

Steps to reproduce:

To reproduce this one, you have to configure outgoing and incoming server and mail aliases

see https://youtu.be/-HzDGh9C9Jc

Current behavior:

If you add a user which has no acces on a object (purchase.order in this case) as follower on a record of this object **AFTER someone has responded by email on this record**, and if you send an message on this record, an exception is raised at the connection of the user added as a follower.

Expected behavior:

No exceptions should be raised at the connection of the user added as a follower.

Video/Screenshot link (optional):

https://youtu.be/-HzDGh9C9Jc

addons/mail/mail_message.py
self.check_access_rule(cr, uid, ids, 'unlink', context=context)
        attachments_to_delete = []
        for message in self.browse(cr, uid, ids, context=context):
            for attach in message.attachment_ids:
                if attach.res_model == self._name and (attach.res_id == message.id or attach.res_id == 0):
                    attachments_to_delete.append(attach.id)
        if attachments_to_delete:
            self.pool.get('ir.attachment').unlink(cr, uid, attachments_to_delete, context=context)
        return super(mail_message, self).unlink(cr, uid, ids, context=context)
    
    
    
    def _notify(self, cr, uid, newid, context=None, force_send=False, user_signature=True):
        """ Add the related record followers to the destination partner_ids if is not a private message.
            Call mail_notification.notify to manage the email sending
        """
        notification_obj = self.pool.get('mail.notification')
        message = self.browse(cr, SUPERUSER_ID, newid, context=context)
        partners_to_notify = set([])
        
        if message.subtype_id and message.model and message.res_id:
            fol_obj = self.pool.get("mail.followers")
            
            fol_ids = fol_obj.search(
                cr, SUPERUSER_ID, [
                    ('res_model', '=', message.model),
                    ('res_id', '=', message.res_id),