Nevertheless, in my experience, ISPs will unblock port 25 for customers on request. I've only worked with a few in my years, but I've not yet encountered any resistance.
Most ISPs that I'm familiar with won't unblock common server ports (25, 80, 443) unless you are on a business account (though that's not much more these days).
Though it isn't always just inbound 25 traffic... often it's outbound as well. Also, the larger issue is hacked/pwned machines and bots, not just open relays. Which reminds me, I need to update Tomato on my router.
My ISP only blocks common ports on dynamic ip ranges. If you order a static IP, you do whatever you want with it. They even set reverse dns record for me when I asked, because some blocklists/mail servers want it that way.
Issue with running your own mail server nowadays is spam. Gmail does a decent job filtering all the crap.
