diff --git a/mail_activity/models/mail_message.py b/mail_activity/models/mail_message.py
new file mode 100644
index 00000000..48222ceb
--- /dev/null
+++ b/mail_activity/models/mail_message.py
@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+# © 2017 Therp BV <http://therp.nl>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+from openerp import fields, models
+
+
+class MailMessage(models.Model):
+    _inherit = 'mail.message'
+
+    mail_activity_type_id = fields.Many2one(
+        'mail.activity.type', 'Mail Activity Type', index=True,
+        ondelete='set null',
+    )