BTW -- here's why transit traffic to port 25 is disallowed:

Most folks who have only seen the recent shiney face on the whole TCP/IP networking world don't see that there's facilities and protocols dating from the late 70's and 80's in there. SMTP is one of them.

You can send email completely anonymously via unsecured SMTP servers simply by using "telnet" to connect to them. Here's some fun for you:

Pick a SMTP server, especially one run at a ISP that isn't super-tight with their security. Let's say, oh, the email server is at "mail.foobar.com"

So, light up a MS-DOS command window on your Windoze PeeCee and do the following: (commands are in bold, comments in italics, server responses in underline)

telnet mail.foobar.com 25  we try to open a TCP connection to port 25 on the named host...

if the host has a server running and listening on port 25, you'll get an answer that might look like this (if it's a Windoze server)

220 foobar.com (server name, version string) NT-ESMTP Server X1

Then if you're being a nice guy, you enter

quit

your command probably won't be echo'ed back to you, when you hit CR, the server comes back with

221 Closing connection. Good bye.

You could also enter "HELP" and hit return and some unsecure servers will come back with a one or two-line response of all the four-letter commands they'll recognize. You can actually send email without any "From" line by telnet'ing to a SMTP server; all that you'd see when you read the message is a "sender" RFC-822 header of the hostname and domain. All the SMTP commands are four letters, because the guys who wrote the original SMTP code tried to be clever, upper-case all the input as it was happening and then use a longword comparison instead of a string compare on the commands. Ancient TOPS-20 and Unix history, but there you are. The reason why you have ISP's putting in an ACL to prevent port 25 connections crossing their network is because of how sendmail was originally written so that it you could send email without any email client.

The way spammers flood their traffic out into the world all too often now is to buy a SMTP "blaster" that connects to port 25 on some hapless machine somewhere, install it on a laptop, wander into a wireless network where they can connect to port 25 on some target server somewhere in the world, they connect to the victim server, fills up the inbound spool on the server with multiple messages and (literally) a million or more "to" addresses per message, then they close the connection and split. The wireless ISP's IP addresses show up in the sendmail and TCP connection logs on the victim server, the wireless ISP gets a hoppin' mad complaint, because the victim sendmail server host gets some even madder complaints, and the result is that the ISP tosses an ACL on their BGP peering point to disallow outbound connections to port 25 from any but their designated email host IP address, the victim sendmail server admin gets smart and tightens up their sendmail configuration and people like you, who are honest users, get shut out of using your SMTP client.