the changes you did do not hurt, but they will not solve your problem. If your server sends out spam and was configured properly before, there are 3 possible reasons:
1) Your server configuration changed and it is now an open relay. You can esaily test this here:
2) One of your smtp / pop3 accounts is misused for sending spam e.g. because someone got a password or cracked a passord of one of your users. To find this out, you have to read your mail log and check it if a user that sends out spam authenticates itself first.
3) The most common reason is not even related to your postfix setup. You might have a vulnerable contact form or cms system in one of the websites on your server that is misused to send spam. To find out which of the webs is causing this, you can use this logging setup: