Incoming SPAM to mail alias not signed as spam

[lexart]

Helo, I have a big problem with spam assasin settings. I am using ISPConfig 3, installed same as in manual "Perfect server Centos"

I have mailbox
name@example.com

and its alias
alias@example.com

When I receive spam to name@example.com, it is correctly signed as spam. BUT when I receive the same spam to alias@example.com, it jumps to Incoming mail folder, with no sign of spam. I've looked over the log and the mail is scanned, signed as spam, but then when it moves to incoming mail folder the sign disappears and mail is magically clear
I have mailbox full of not signed spam, I need to solve this. Can anyone help me please? Thank you very much.