qmail - mail server hacked,sending spam - help.. >

Hello, I have problem with one of my mail servers…,
I am using qmail , from 2 days I notice that there is huge load average on the server - 9 and up …, I stopped its wlan access , when I look at the top table the mail services make big load average, and when I stop qmail the average stops. (qmailctl stop) …
So I checked the queues of qmail, and saw that My server actually is sending hundreds of mails :confused: (last time where 1000+), I deleted them and it starts to send again more and more…,
My problem is that I can’t locate the source of the hack, where should I look to stop the process which makes my server sending SPAM…

Guess number one - you’ve misconfigured your system to be an open relay - this means anyone can connect and relay mail via your system.

Go here;
Check an Open Relay

Input the name or IP of your server - if you have open relays, close it ASAP.