For some reason I don't have a /etc/hosts folder (I wasn't in charge of the initial setup). The server is running Ubuntu. I am not sure what SELinux is.
Oh yeah, I also recently got Roundcube to be able to recieve mail but still not send. (I am not sure how, but I fiddled around with making a sub domain site(e.g. mail.domain.net) and when I added email users to this site they are able to recieve messages.)
Also, might it have anything to do with the External/local mailserver option in ispconfig? Will it help if I configure Roundcube to use my dsl smtp service provided by verizon if possible or should I stick to using "localhost" in smtp option? (As you might tell I am somewhat of a newbie regarding this subject).