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
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import logging
from openerp import tools
from email.header import decode_header
from email.utils import formataddr
from openerp import SUPERUSER_ID, api
from openerp.osv import osv, orm, fields
from openerp.tools import html_email_clean
from openerp.tools.translate import _
from HTMLParser import HTMLParser
_logger = logging.getLogger(__name__)
""" Some tools for parsing / creating email fields """
def decode(text):
    """Returns unicode() string conversion of the the given encoded smtp header text"""
    if text:
        text = decode_header(text.replace('\r', ''))
        
        
        return ' '.join([tools.ustr(x[0], x[1]) for x in text])
class MLStripper(HTMLParser):
    def __init__(self):