first let me give you a nice welcome to Linux Junior - I hope we can be of help.
are you using it as a sendmail replacement or as a pop mail server? If a pop mail server then look at the files in /etc/xinitd.d/ - there are a bunch of files and each one cooresponds to a different service, as user root open a file in the editor of your choice and edit the ones which look like they may be affecting your mail server - in the file there is a line which says
disable = XXX
change whatever the XXX is to no, you may need to do this to a few files.
i am not positive if this will work since i have not used qmail. you may want to ask this in the server and netwroking formum.
hope that helps.