diff --git a/addons/crm/models/crm_lead.py b/addons/crm/models/crm_lead.py
index b3adb24281f..d7d352b4efb 100644
--- a/addons/crm/models/crm_lead.py
+++ b/addons/crm/models/crm_lead.py
@@ -1306,6 +1306,11 @@ class Lead(models.Model):
             through message_process.
             This override updates the document according to the email.
         """
+
+        # remove external users
+        if self.env.user.has_group('base.group_portal'):
+            self = self.with_context(default_user_id=False)
+
         # remove default author when going through the mail gateway. Indeed we
         # do not want to explicitly set user_id to False; however we do not
         # want the gateway user to be responsible if no other responsible is