diff --git a/api.py b/api.py
index be83784..16a4880 100644
--- a/api.py
+++ b/api.py
@@ -27,7 +27,7 @@ from cosmopolite.lib import utils
 import config
 
 
-def CreateChannel(google_user, client, instance_id, args):
+def CreateChannel(google_user, client, client_address, instance_id, args):
   models.Instance.FindOrCreate(instance_id)
 
   token = channel.create_channel(
@@ -52,7 +52,7 @@ def CreateChannel(google_user, client, instance_id, args):
   }
 
 
-def Pin(google_user, client, instance_id, args):
+def Pin(google_user, client, client_address, instance_id, args):
   instance = models.Instance.FromID(instance_id)
   if not instance or not instance.active:
     # Probably a race with the channel opening
@@ -69,6 +69,7 @@ def Pin(google_user, client, instance_id, args):
         message,
         models.Client.profile.get_value_for_datastore(client),
         sender_message_id,
+        client_address,
         instance)
   except models.DuplicateMessage:
     logging.warning('Duplicate pin: %s', sender_message_id)
@@ -86,7 +87,7 @@ def Pin(google_user, client, instance_id, args):
   }
 
 
-def SendMessage(google_user, client, instance_id, args):
+def SendMessage(google_user, client, client_address, instance_id, args):
   subject = args['subject']
   message = args['message']
   sender_message_id = args['sender_message_id']
@@ -95,7 +96,8 @@ def SendMessage(google_user, client, instance_id, args):
     models.Subject.FindOrCreate(subject).SendMessage(
         message,
         models.Client.profile.get_value_for_datastore(client),
-        sender_message_id)
+        sender_message_id,
+        client_address)
   except models.DuplicateMessage:
     logging.warning('Duplicate message: %s', sender_message_id)
     return {
@@ -112,7 +114,7 @@ def SendMessage(google_user, client, instance_id, args):
   }
 
 
-def Subscribe(google_user, client, instance_id, args):
+def Subscribe(google_user, client, client_address, instance_id, args):
   instance = models.Instance.FromID(instance_id)
   subject = models.Subject.FindOrCreate(args['subject'])
   messages = args.get('messages', 0)
@@ -141,7 +143,7 @@ def Subscribe(google_user, client, instance_id, args):
   }
 
 
-def Unpin(google_user, client, instance_id, args):
+def Unpin(google_user, client, client_address, instance_id, args):
   instance = models.Instance.FromID(instance_id)
   subject = args['subject']
   sender_message_id = args['sender_message_id']
@@ -162,7 +164,7 @@ def Unpin(google_user, client, instance_id, args):
   }
 
 
-def Unsubscribe(google_user, client, instance_id, args):
+def Unsubscribe(google_user, client, client_address, instance_id, args):
   instance = models.Instance.FromID(instance_id)
   subject = models.Subject.FindOrCreate(args['subject'])
   models.Subscription.Remove(subject, instance)
@@ -199,6 +201,7 @@ class APIWrapper(webapp2.RequestHandler):
       result = callback(
           self.verified_google_user,
           self.client,
+          self.request.remote_addr,
           self.request_json['instance_id'],
           command.get('arguments', {}))
       # Magic: if result contains "events", haul them up a level so the
diff --git a/lib/models.py b/lib/models.py
index fb2388a..856f0ae 100644
--- a/lib/models.py
+++ b/lib/models.py
@@ -175,7 +175,7 @@ class Subject(db.Model):
     return list(query)
 
   @db.transactional()
-  def PutMessage(self, message, sender, sender_message_id):
+  def PutMessage(self, message, sender, sender_message_id, sender_address):
     """Internal helper for SendMessage().
 
     Unless/until channel.send_message becomes transactional, we have to finish
@@ -205,6 +205,7 @@ class Subject(db.Model):
         message=message,
         sender=sender,
         sender_message_id=sender_message_id,
+        sender_address=sender_address,
         id_=message_id)
     obj.put()
 
@@ -222,15 +223,17 @@ class Subject(db.Model):
         readable_only_by != reader):
       raise AccessDenied
 
-  def SendMessage(self, message, sender, sender_message_id):
+  def SendMessage(self, message, sender, sender_message_id, sender_address):
     self.VerifyWritable(sender)
-    obj, subscriptions = self.PutMessage(message, sender, sender_message_id)
+    obj, subscriptions = self.PutMessage(
+        message, sender, sender_message_id, sender_address)
     event = obj.ToEvent()
     for subscription in subscriptions:
       subscription.SendMessage(event)
 
   @db.transactional()
-  def PutPin(self, message, sender, sender_message_id, instance):
+  def PutPin(self, message, sender, sender_message_id,
+             instance, sender_address):
     """Internal helper for Pin()."""
     # sender_message_id should be universal across all subjects, but we check
     # it within just this subject to allow in-transaction verification.
@@ -248,15 +251,16 @@ class Subject(db.Model):
         message=message,
         sender=sender,
         sender_message_id=sender_message_id,
+        sender_address=sender_address,
         instance=instance)
     obj.put()
 
     return (obj, list(Subscription.all().ancestor(self)))
 
-  def Pin(self, message, sender, sender_message_id, instance):
+  def Pin(self, message, sender, sender_message_id, sender_address, instance):
     self.VerifyWritable(sender)
     obj, subscriptions = self.PutPin(
-        message, sender, sender_message_id, instance)
+        message, sender, sender_message_id, instance, sender_address)
     event = obj.ToEvent()
     for subscription in subscriptions:
       subscription.SendMessage(event)
@@ -347,6 +351,7 @@ class Message(db.Model):
   message = db.TextProperty(required=True)
   sender = db.ReferenceProperty(required=True, reference_class=Profile)
   sender_message_id = db.StringProperty(required=True)
+  sender_address = db.StringProperty(required=True)
   # id is reserved
   id_ = db.IntegerProperty(required=True)
 
@@ -367,9 +372,10 @@ class Pin(db.Model):
 
   created = db.DateTimeProperty(required=True, auto_now_add=True)
   instance = db.ReferenceProperty(required=True, reference_class=Instance)
-  sender = db.ReferenceProperty(required=True, reference_class=Profile)
   message = db.TextProperty(required=True)
+  sender = db.ReferenceProperty(required=True, reference_class=Profile)
   sender_message_id = db.StringProperty(required=True)
+  sender_address = db.StringProperty(required=True)
 
   def ToEvent(self, event_type='pin'):
     return {