So, I've taken a couple of stabs at this, and I think the closest you'll get is a content filter with a regex that looks for a URL that has "@yourdomain" in it.
The issue is that for both content filters and message filters, you can't use the variables that you can use for actions.
Content filter conditions are processed in order, so to minimize how many messages get the full regex scan run across them you could have the first condition in the filter be a URL reputation check for low reputation, and then the regex against the message body and set it for all conditions must match. That way, if it's a high reputation, you don't scan the email for the regex.
