diff --git a/addons/portal/__init__.py b/addons/portal/__init__.py
index 0045a557a49..e7026986ea4 100644
--- a/addons/portal/__init__.py
+++ b/addons/portal/__init__.py
@@ -21,6 +21,7 @@
 
 import portal
 import mail_mail
+import mail_message
 import wizard
 import acquirer
 
diff --git a/addons/portal/mail_message.py b/addons/portal/mail_message.py
new file mode 100644
index 00000000000..38516268c24
--- /dev/null
+++ b/addons/portal/mail_message.py
@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+##############################################################################
+#
+#    OpenERP, Open Source Management Solution
+#    Copyright (C) 2004-2011 OpenERP S.A (<http://www.openerp.com>).
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU Affero General Public License as
+#    published by the Free Software Foundation, either version 3 of the
+#    License, or (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU Affero General Public License for more details.
+#
+#    You should have received a copy of the GNU Affero General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+##############################################################################
+
+from openerp.osv import osv, orm
+from openerp.tools.translate import _
+
+
+class mail_message(osv.Model):
+    """ Update of mail_message class, to restrict mail access. """
+    _inherit = 'mail.message'
+
+    def _search(self, cr, uid, args, offset=0, limit=None, order=None,
+        context=None, count=False, access_rights_uid=None):
+        """ Override that adds specific access rights of mail.message, to remove
+            all no discussion message if uid is a portal user.
+        """
+        group_ids = self.pool.get('res.users').browse(cr, uid, uid, context=context).groups_id
+        if any(group.is_portal for group in group_ids):
+            subtype_id = self.pool.get("ir.model.data").get_object_reference(cr, uid, 'mail', 'mt_comment')[1]
+            args = ['&', ('subtype_id', '=', subtype_id)] + args
+
+        return super(mail_message, self)._search(cr, uid, args, offset=offset, limit=limit, order=order,
+            context=context, count=False, access_rights_uid=access_rights_uid)
+
+    def check_access_rule(self, cr, uid, ids, operation, context=None):
+        """ Add Access rules of mail.message for portal user:
+            - read:
+                - raise if the type is not 'comment' or 'email'
+        """
+        group_ids = self.pool.get('res.users').browse(cr, uid, uid, context=context).groups_id
+        if any(group.is_portal for group in group_ids):
+            subtype_id = self.pool.get("ir.model.data").get_object_reference(cr, uid, 'mail', 'mt_comment')[1]
+            cr.execute('SELECT DISTINCT id FROM "%s" WHERE subtype_id != %s AND id = ANY (%%s)' % (self._table, subtype_id), (ids,))
+            if cr.fetchall():
+                raise orm.except_orm(_('Access Denied'),
+                        _('The requested operation cannot be completed due to security restrictions. Please contact your system administrator.\n\n(Document type: %s, Operation: %s)') % \
+                        (self._description, operation))
+
+        return super(mail_message, self).check_access_rule(cr, uid, ids=ids, operation=operation, context=context)