Okay, here are my $0.02...

Your ISP prevents you to connect to ANY "25" port (SMTP port) of any server... What you could do is setup a port forwarder on your linux box and have that connect to the remote SMTP server (port 25)... HOWEVER, this would not work, assuming that that linux box is on the same isp...

Goto http://portfwd.sourceforge.net/ and get their RPM package...

Here are my instructions...

Login to your server as root, then:

Get the RPM package: wget http://prdownloads.sourceforge.net/p...-1rh6.i386.rpm

Install the RPM: rpm -U ./portfwd-0.22-1rh6.i386.rpm

Edit the config file: pico /etc/portfwd.cfg

Now add the following lines:
Okay, now, start (or reboot the server) the portfwd: /usr/sbin/portfwd -c /etc/portfwd.cfg

Goto outlook or whatever you use, and set as SMTP server: yourdomain.com on port (SMTP port) 2500

Now try and send a mail...Should work, let me know if it fails..