When I set up email redirects within Plesk 9.5, Spamassassin ignores all emails sent to the redirected address and only scans emails that are sent directly to the address which has a mailbox.
Steps to reproduce
Set up two mail accounts: email@example.com as a proper email account with a mailbox and firstname.lastname@example.org with all emails redirected to email@example.com. (It doesn't make a difference, if firstname.lastname@example.org has a mailbox enabled or not.)
email@example.com -> firstname.lastname@example.org
Set up the spam filter on both accounts. I set mine to delete spam right away, but you can just keep the default ("mark as spam").
Now, when you send an emails to email@example.com, it will have Spamassassins tags in the email header, but when you send emails to firstname.lastname@example.org, they will end up in the same mailbox but will have no spamassassin tags in the emails header and they will not be scanned.
I am using Plesk 9.5.4 on Ubuntu 8.04 LTS with the default Qmail.
I've observed this bug since Plesk 8, but I can't stand it any more and would appreciate any hack or fix.