OS related topics
From OpenCms Wiki
Email problem on OpenCMS 7.0.4 installed on CentOS5.3/Tomcat 5.5.27
you cannot send out email after default installation (I'll post the error message later). All you need to do is to delete /var/lib/tomcat5/webapps/ROOT/WEB-INF/lib/mail.jar (assuming you install opencms as ROOT to eliminate the /opencms/opencms). Then OpenCMS will use the $tomcat5$/common/lib/[javamail].jar to send out email. Email works then.
Of course, you need to have sendmail installed on CentOS.