I dont want to modify the subject, how can I still recognize if my message is spam?

Besides the possiblities of modifying the subject, or even denying the message completely, Pinjo will always mark the message with an extra header value in the mailmessage.
This headervalue is normally invisible for the user but can be used for additional filtering in your mailclient. This header, named X-Spam-Status can have the values Negative for non-spam, and Positive for spam. In this way its possible to recognize a message without modifying the subject.