SpamAssassin changes Postfix headers

Adding Spamassassin to my Postfix has had an unwarnted effect on my email headers. We use Postfix with all of the mail routed to a catchall account. Our virtual_alias_maps file looks something like: @mydomain.com catchall @mydomain2.com catchall @mydomain3.com catchall ... If a message is sent to two addresses in our domain, we'll get two messages delivered to the catchall, the first one with headers like: X-Original-To: a1@mydomain.com Delivered-To: a1@mydomain.com To: a1@mydomain.com, a2@mydomain.com and the second on with headers like: X-Original-To: a2@mydomain.com Delivered-To: a2@mydomain.com To: a1@mydomain.com, a2@mydomain.com This is exactly what we want. We can look at the X-Original-To or the Delivered-To to know who was the original recipient of the message. However, when we turn SpamAssassin on, the headers are modified so that both messages look like: X-Original-To: catchall@mydomain.com Delivered-To: catchall@mydomain.com To: a1@mydomain.com, a2@mydomain.com and there is absolutely nothing in the message that lets me know which one was for which recipient. Is there a way to stop SpamAssassin from modifying the headers? If not, is there another way to preserve the identity of the original recipient?