Filter relayed mail

I'd like to filter email before sending it on to a third party server:
ispconfig (3.2.5) server -> spamassassin -> third party server.

Here's what I've tried:

1. Adding the domain and third party server to Relay Recipient (Email > Email Accounts > Email Routing)
2. Adding the domain to Email > Global Filters > Relay Recipients

This works, in that it relays the email and it arrives on the third party server, but I'd also like to scan it for viruses and drop spam before sending it on. So I tried:

1. Adding the domain to Email > Spamfilter > User / Domain

mail continues to flow, but I'm not seeing the spam filter headers that I'm expecting.

Is there a way to configure this in ISPConfig?
Thanks

 

Server={I chose the name of the ISPConfig server from the dropdown, there is only one}
Priority=5
Policy=Normal
Email (Pattern)=@{the domain I'm trying to filter emails for}
Name=blah
Local=Yes

(The one I wasn't sure about was the Local setting. The manual says 'This specifies if this record is active (Yes) or not (No)', so I set it to Yes.)

 

Eventually managed to test this. The emails get forwarded but they still don't get a spam score / get filtered.