But how can my server use another port, when it has to send messages to other servers which are using the standard port 25?
That very traffic will be blocked by my ISP -- because although I have both 25 and 26 open, my server will have to communicate with the other servers on the standard SMTP port, 25.
If my users needed to bypass this kind of blocking, they could contact my server -- but my server itself needs to be able to send e-mails itself. How can it do that if the only standard port is blocked?
For instance, my webhost (Spry.com) is running 2 copies of the mail server -- on ports 25 and 26. That allows me to send mail from that domain name, because my computer and the webserver talk on port 26 -- which isn't blocked by SBCYahoo (DSL). But the server there has to send it to its destination -- so what if THAT server was connected to the Internet via SBCYahoo? Could it ever hope to send out e-mails?
Another way of looking at it -- if blocking port 25 is to prevent spamming, why wouldn't spammers just set up a cheap Linux box and configure it for port 26, and send out spam 24/7? Is it really that simple?
Last edited by AgeOfPenguins-com; 10th May 2006 at 23:44.