If you have too much good senders blocked (even if you are forwarding the errors to assp-notspam@yourdomain.com), you can decrease the sensibility of your antispam lowering it from normal to low, lower or lowest. If you decrease the spam sensibility some spam could pass, however you strongly reduce the risk to block a good email.
If good senders are often blocked also with low, lower and lowest setting even if you are forwarding the errors to assp-notspam@yourdomain.com please check the email headers, probably the sender is blacklisted or his ip could be blocked at early stage and you should contact our technical support to check it further.
