Increasing spam level to backup MX

[Davide Marchi]

Hi Friends,

activating a backup server I realized that some spammers using this 
server to send spam to my relay_recipient_maps addresses. Spam is then 
successfully forwarded to the main server.

Is there a parameter to prevent this type of action? A type check "do 
not receive email if the main server is reachable...?

Or should I operate directly by SpamAssassin?

many many thanks



Davide