Ashamed

I must confess something.
Though I have toyed with Linux for some time, I set my main domain
server up as an NT box because at least I know how to configure e-mail
with it.
I'm running a program out of New Zealand called DWatch that for 5 users
or less, is free.
I tried setting my server up running Mandrake Linux 7 and every time I
tried to send e-mail to a defined user, it would give an error message
back saying something to the effect of now relaying allowed.
At that time, I was not trying to relay, I was merely trying to send a
message to a registered user.
In frustration I reinstalled NT Server and installed DWatch which is
free for 5 users or less.
I don't want a big domain, or anything. I registered pamarq.com just to
learn more.
I wanted to run Linux on it, but could not because I didn't have the
know-how to set up Sendmail.
My main PC is running Linux with VMWare clients of Windows applications
primarily for my wife.
I want my server to be running Linux too, but have not found a simple
e-mail (pop3/smtp) program that is easy to configure within Linux.
Here is what I want:
2 or 3 users being able to log into pamarq.com (currently I have
mark@pamarq.com, mmyers@pamarq.com and pamela@pamarq.com). I also want
to be able to relay within my personal domain at fastq plus one other IP
address which is the firewall IP address of my company.
That is it. Nothing fancy.
I could figure out how to do this with DWatch for NT, but is there
something simple that I could run on Linux that would do the same thing?
I don't need heavy duty. I just want to prevent spammers from using my
server, but in the same way, I want to be able to relay from my server
while at work (my IP address for our firewall never changes).
Please help if you can help me to figure out a simple solution with
Linux.
I'm not an absolute novice, but I don't need anything fancy either.
At work I'm an NT administrator so I run a 100% Microsoft network (not
my choice). I was even told today to take the Linux server off that
monitored Internet usage.
So I need to be able to relay from 1 IP address from the Internet, and a
range of IP address (192.168.204.2*) (fictional) from home.
I don't want to run a business per se, nor do I want to run an ISP. I
just want to learn.
Any advice would be helpful.
Thanks!
Mark Myers