getting my website send newsletters or emails

hello everyone The website am working on is built on codeigniter framework.It allows for emails to be send by default using mail, sendmail, or smtp protocol.Initially I successfully used mail for protocol but days after nothing was working and any attempts to use smtp is also a failure. In my research, I came to this forum and read about WHM which i didn't know before.What i wish to know are the various steps to setup the smtp protocol working for the site.what do i do on WHM, cpanel, etc? Thanks for your help.