diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 336959094b..14ef535b27 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -33,6 +33,7 @@ class RegistrationConfig(Config):
 
         self.registrations_require_3pid = config.get("registrations_require_3pid", [])
         self.allowed_local_3pids = config.get("allowed_local_3pids", [])
+        self.check_is_for_allowed_local_3pids = config.get("check_is_for_allowed_local_3pids", False)
         self.registration_shared_secret = config.get("registration_shared_secret")
 
         self.bcrypt_rounds = config.get("bcrypt_rounds", 12)
@@ -63,6 +64,10 @@ class RegistrationConfig(Config):
         # Mandate that users are only allowed to associate certain formats of
         # 3PIDs with accounts on this server.
         #
+        # Use an Identity Server to establish which 3PIDs are allowed to register?
+        # Overrides allowed_local_3pids below.
+        # check_is_for_allowed_local_3pids: matrix.org
+        #
         # allowed_local_3pids:
         #     - medium: email
         #       pattern: ".*@matrix\\.org"
@@ -71,6 +76,7 @@ class RegistrationConfig(Config):
         #     - medium: msisdn
         #       pattern: "\\+44"
 
+
         # If set, allows registration by anyone who also has the shared
         # secret, even if registration is otherwise disabled.
         registration_shared_secret: "%(registration_shared_secret)s"
diff --git a/synapse/util/threepids.py b/synapse/util/threepids.py
index 75efa0117b..cd629c2ec9 100644
--- a/synapse/util/threepids.py
+++ b/synapse/util/threepids.py
@@ -16,9 +16,12 @@
 import logging
 import re
 
+from twisted.internet import defer
+
 logger = logging.getLogger(__name__)
 
 
+@defer.inlineCallbacks
 def check_3pid_allowed(hs, medium, address):
     """Checks whether a given format of 3PID is allowed to be used on this HS
 
@@ -28,9 +31,20 @@ def check_3pid_allowed(hs, medium, address):
         address (str): address within that medium (e.g. "wotan@matrix.org")
             msisdns need to first have been canonicalised
     Returns:
-        bool: whether the 3PID medium/address is allowed to be added to this HS
+        defered bool: whether the 3PID medium/address is allowed to be added to this HS
     """
 
+    if hs.config.check_is_for_allowed_local_3pids:
+        data = yield hs.http_client.get_json(
+            "https://%s%s" % (
+                hs.config.check_is_for_allowed_local_3pids,
+                "/_matrix/identity/api/v1/discover_urls"
+            ),
+            {'medium': medium, 'address': address }
+        )
+        defer.returnValue(data.hs_url+"/" == self.hs.config.public_baseurl)
+        return
+
     if hs.config.allowed_local_3pids:
         for constraint in hs.config.allowed_local_3pids:
             logger.debug(
@@ -41,8 +55,11 @@ def check_3pid_allowed(hs, medium, address):
                 medium == constraint['medium'] and
                 re.match(constraint['pattern'], address)
             ):
-                return True
+                defer.returnValue(True)
+                return
     else:
-        return True
+        defer.returnValue(True)
+        return
 
-    return False
+    defer.returnValue(False)
+    return