ok lets start with the easy one
2a) you can do it on your own - perfect
2b) To setup postfix to listen on a different port the following has to be done
First add a line in /etc/services
This line schould look like
wich means smtpReRoute should listen on port 8025/tcp
Next you have to configure /etc/postfix/master.cf
Change the line where it says
smtp inet y/n y/n y/n - - smtpd
smtprr inet y/n y/n y/n - - smtpd
y/n - may vary on your machine
finally restart postfix.
Now you have an working MTA on port 8025
As I said it only will work for your LAN/WAN
And now the tricky things. I will try to give easy common examples for the most interesting lines.
1) All Lines are within main.cf
myhostname = swiftsmart.no-ip.org
mydomain = swiftsmart.no-ip.org
mydestination = $myhostname, localhost.$mydomain, $mydomain
mynetworks = x.x.x.x/xx, 127.0.0.0/8, y.y.y.y/32
where x.x.x.x/xx ist your local inet like 192.168.0.1/24
and y.y.y.y is the one ip you got form your ISP
For a first test this should be enough. Postfix should now as a mail server for your domain. Now you have to create lokal users on the machine like mybuddy
his e-mail would be firstname.lastname@example.org
With two configured MUA´s you can test deliveries.
One thing you should always do when configuring with postfix. In shell call the command
tail -f /var/log/messages
this will give usefull information on the mail server
I would say give it a shoot.