CentOS/Cpanel Help

I need assistance with a CentOS Linux server with WHM. I would like for the server not to have spam go through it, also for server to generate ssl for certain sites as there is an error when sending emails that says cert. is insecure. Also to find why space on accounts fill up (If its because of spam/viruses etc.) Also other general security tweaks/enquiries. ## Deliverables Essentially all I require is: - Security Tweak/Optimising - Ensuring spam doesnt go through server - Finding out why a user account has gone over its space (What caused it) - Why server has CPU Spikes - Ever since mail was made to be using SMTP there is a message that says it is untrusted, so to fix that. - Making sure even with any changes in mail users are still able to send mail via forums etc.