diff --git a/lib/oversip/modules/outbound_mangling.rb b/lib/oversip/modules/outbound_mangling.rb
index c8a9bef..0294d16 100644
--- a/lib/oversip/modules/outbound_mangling.rb
+++ b/lib/oversip/modules/outbound_mangling.rb
@@ -6,15 +6,27 @@ module OutboundMangling
 
     @log_id = "OutboundMangling module"
 
-    def self.add_outbound_to_contact request
-      if request.contact and request.connection_outbound_flow_token
-        log_system_debug "performing Contact mangling (adding ;ov-ob Outbound param) for #{request.log_id}"  if $oversip_debug
+    def self.add_outbound_to_contact proxy
+      unless proxy.is_a? ::OverSIP::SIP::Proxy
+        raise ::OverSIP::RuntimeError, "proxy must be a OverSIP::SIP::Proxy instance"
+      end
 
-        # Add the ;ov-ob param to the Contact URI.
-        request.contact.set_param "ov-ob", request.connection_outbound_flow_token
-        return true
-      else
-        return false
+      proxy.on_target do |target|
+        request = proxy.request
+        # Just act in case the request has a single Contact, its connection uses Outbound
+        # and  no ;ov-ob param exists in Contact URI.
+        if request.contact and request.connection_outbound_flow_token and not request.contact.has_param? "ov-ob"
+          log_system_debug "performing Contact mangling (adding ;ov-ob Outbound param) for #{request.log_id}"  if $oversip_debug
+
+          request.contact.set_param "ov-ob", request.connection_outbound_flow_token
+
+          proxy.on_success_response do |response|
+            if (contacts = response.headers["Contact"])
+              log_system_debug "reverting original Contact value (removing ;ov-ob Outbound param) from response"  if $oversip_debug
+              contacts.each { |contact| contact.gsub! /;ov-ob=[_\-0-9A-Za-z]+/, "" }
+            end
+          end
+        end
       end
     end
 
@@ -39,22 +51,6 @@ def self.extract_outbound_from_ruri request
       end
     end
 
-    def self.remove_outbound_from_contact message
-      unless message.is_a? ::OverSIP::SIP::Message
-        raise ::OverSIP::RuntimeError, "message must be a OverSIP::SIP::Request or OverSIP::SIP::Response"
-      end
-
-      if (contacts = message.headers["Contact"])
-        log_system_debug "reverting original Contact value (removing ;ov-ob Outbound param) for response"  if $oversip_debug
-        contacts.each do |contact|
-          contact.gsub! /;ov-ob=[_\-0-9A-Za-z]+/, ""
-        end
-        return true
-      else
-        return false
-      end
-    end
-
   end  # module OutboundMangling
 
 end