Which tutorials have you done and what results have to gotten?

I personally used this one:

https://help.ubuntu.com/community/Postfix

I tried that one also. I can't get mail to send with that one. I even
reinstalled windows to try a few with no luck. I ended up reinstalling ubuntu
for a fresh start.

Ok. You cant send to what? Are you sending mail directly or through a smtp
relay?
Post your postfix conf file editing any passwords for us to view.

If you have a dynamic ip you need to look at dyndns or no-ip. I use it for
my own system.

You can't block port 25:

25 TCP Simple Mail Transfer Protocol (SMTP)—used for e-mail routing between
mail servers

I am not sure you can use a dynamic IP, I think you need a static IP. Is this
SMTP server going to be on an intranet or the internet? If you need to SMTP to
servers on the Internet, that is going to be quite a chore. Are you just
experimenting or is this a real server?

If 25 is being blocked you may have to use 587. If you on a dynamic IP. Well my
guess is your not setting behind a router/firewall on your SOHO network. So the
fast way around a dynamic IP is to use a DDNS like no-ip.com or dyndns.com . I
know no-ip has a client for linux. (use it on guilds mumble server). So it
should work for postfix to. Got to love free sub-domains for redirect of
servers.