At first, you need your own domain. Many providers block mail servers on broadband connections, so a DynDNS domain and a home-server may possibly not an option, in that case you need a hosted server. Then you need a mailserver. How to configure a mail-server on CentOS can easily be found with a websearch, for example with the keywords Centos 6 mail server
, which comes up for example with this: http://www.1a-centosserver.com/cento...ail_server.php
I have not used that guide, so I don't know how good it is.