Postfix Backscatter

Hi, my postfix-Mailserver on a SuSE9.1 system ist flooded by backscatter mails which are undeliverable (random addresses). At the moment it is nearly impossible to sent a mail to this system. Yesterday it handled (rejected) about 12.000 of such mails. This seems to be too slow. So i changed my configuration setting: smtpd_error_sleep_time = 0, stopped all RBL usage and increased the number of smtp processes from 2 to 80. Now my system seems to handle about 40.000/day but this is not enough, there is still only a small chance to send a normal mail. Is there any chance to optimize postfix so that it can handle much more mails/connections each day? Or any other idea to solve such backscatter problems? Best Uwe