Necessary patches

I’m running a webmail server. My configoration are RH7.2 , APACHE with SSL, qmail(SMTP),
vpopmail(POP3) and SQWEBmail(web interface). I got SSH (I don’t use it), DNS server and I put ipchains for security. Here is the sad story; my server have beencompromised 3 times so far. What am supposed to do ?
Every time it compromised, it won’t start.I can’t afford to setup the server from scratch again. I thought having linux would make my live easier.
Please anyone from the open source community give good advise to me what should I do next and also an advise to hang on with linux.