diff --git a/addons/mail/mail_message.py b/addons/mail/mail_message.py
index ed90ee6d932..cdf61b043ec 100644
--- a/addons/mail/mail_message.py
+++ b/addons/mail/mail_message.py
@@ -121,7 +121,8 @@ class mail_message(osv.Model):
                  "message, comment for other messages such as user replies"),
         'email_from': fields.char('From',
             help="Email address of the sender. This field is set when no matching partner is found for incoming emails."),
-        'author_id': fields.many2one('res.partner', 'Author',
+        'author_id': fields.many2one('res.partner', 'Author', select=1,
+            ondelete='set null',
             help="Author of the message. If not set, email_from may hold an email address that did not match any partner."),
         'partner_ids': fields.many2many('res.partner', string='Recipients'),
         'notified_partner_ids': fields.many2many('res.partner', 'mail_notification',
@@ -129,14 +130,17 @@ class mail_message(osv.Model):
             help='Partners that have a notification pushing this message in their mailboxes'),
         'attachment_ids': fields.many2many('ir.attachment', 'message_attachment_rel',
             'message_id', 'attachment_id', 'Attachments'),
-        'parent_id': fields.many2one('mail.message', 'Parent Message', select=True, ondelete='set null', help="Initial thread message."),
+        'parent_id': fields.many2one('mail.message', 'Parent Message', select=True,
+            ondelete='set null', help="Initial thread message."),
         'child_ids': fields.one2many('mail.message', 'parent_id', 'Child Messages'),
         'model': fields.char('Related Document Model', size=128, select=1),
         'res_id': fields.integer('Related Document ID', select=1),
         'record_name': fields.function(_get_record_name, type='char',
             store=True, string='Message Record Name',
             help="Name get of the related document."),
-        'notification_ids': fields.one2many('mail.notification', 'message_id', 'Notifications'),
+        'notification_ids': fields.one2many('mail.notification', 'message_id',
+            string='Notifications',
+            help='Technical field holding the message notifications. Use notified_partner_ids to access notified partners.'),
         'subject': fields.char('Subject'),
         'date': fields.datetime('Date'),
         'message_id': fields.char('Message-Id', help='Message unique identifier', select=1, readonly=1),
@@ -144,7 +148,8 @@ class mail_message(osv.Model):
         'to_read': fields.function(_get_to_read, fnct_search=_search_to_read,
             type='boolean', string='To read',
             help='Functional field to search for messages the current user has to read'),
-        'subtype_id': fields.many2one('mail.message.subtype', 'Subtype'),
+        'subtype_id': fields.many2one('mail.message.subtype', 'Subtype',
+            ondelete='set null', select=1,),
         'vote_user_ids': fields.many2many('res.users', 'mail_vote',
             'message_id', 'user_id', string='Votes',
             help='Users that voted for this message'),