diff --git a/addons/mail/mail_thread.py b/addons/mail/mail_thread.py
index 8e5c2697797..f32f184e079 100644
--- a/addons/mail/mail_thread.py
+++ b/addons/mail/mail_thread.py
@@ -445,12 +445,13 @@ class mail_thread(osv.osv):
             'partner_address_id': False,
             'partner_id': False
         }
-        email = to_email(email)[0]
-        address_ids = address_pool.search(cr, uid, [('email', '=', email)])
-        if address_ids:
-            address = address_pool.browse(cr, uid, address_ids[0])
-            res['partner_address_id'] = address_ids[0]
-            res['partner_id'] = address.partner_id.id
+        if email:
+            email = to_email(email)[0]
+            address_ids = address_pool.search(cr, uid, [('email', '=', email)])
+            if address_ids:
+                address = address_pool.browse(cr, uid, address_ids[0])
+                res['partner_address_id'] = address_ids[0]
+                res['partner_id'] = address.partner_id.id
         return res
 
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