Your IP address is listed in CBL as psam sender:
http://cbl.abuseat.org/lookup.cgi?ip=85.82.7.54
Thats why the server refuses your emails. Please check that your server is not a open relay and check that you do not have PHP or perl formmail scripts installed on your server that allow mail relaying.
With the command postqueue -p you can check how many mails are stored in your mailqueue.