I have sendmail with procmail and SA running fine, gets all my spam. However I have a user that forwards his email via virtusertable, since he is not a real system user, and it seems that all the spam he gets being forwarded as well.
Is there a way in sendmail to make it pass through SA and then forward?
You can use a sendmail milter, like mimedefang, or any MTA layer integration tool, like MailScanner, to call spamassassin instead of doing the quick-and-easy procmail call.
As a side benefit, most of these tools make it easy to call clamav so you can get some free MTA-layer virus scanning while you're at it.
