Allow HS to send emails when adding an email to the HS (#6042)

synapse/push/mailer.py

@@ -179,6 +179,35 @@ class Mailer(object):
             template_vars,
         )
 
+    @defer.inlineCallbacks
+    def send_add_threepid_mail(self, email_address, token, client_secret, sid):
+        """Send an email with a validation link to a user for adding a 3pid to their account
+
+        Args:
+            email_address (str): Email address we're sending the validation link to
+
+            token (str): Unique token generated by the server to verify the email was received
+
+            client_secret (str): Unique token generated by the client to group together
+                multiple email sending attempts
+
+            sid (str): The generated session ID
+        """
+        params = {"token": token, "client_secret": client_secret, "sid": sid}
+        link = (
+            self.hs.config.public_baseurl
+            + "_matrix/client/unstable/add_threepid/email/submit_token?%s"
+            % urllib.parse.urlencode(params)
+        )
+
+        template_vars = {"link": link}
+
+        yield self.send_email(
+            email_address,
+            "[%s] Validate Your Email" % self.hs.config.server_name,
+            template_vars,
+        )
+
     @defer.inlineCallbacks
     def send_notification_mail(
         self, app_id, user_id, email_address, push_actions, reason