Questions on hosting

Ok i bought a domain, we will call it domain.com. I have been running mysql server, php and apache smoothly. I wanted to add a email server to my domain. The domain serve ris just set to relay to my ip address on my server. I want to be able to send outgoing mail, as which i can do with some programs, but i also want to recieve mail through this address. Ex. webmaster@domain.com. I cant figure out how exactly the mail servers work. Ive been able to send mail sucessfully but not been able to return mail. Im nto worried about remote access or anything, but what program should i use and how do i set it up to recieve mail from webmaster@domain.com. Any suggestions. Also i have my dns server setup not to mask my ip address, will this cause any conflicts?