Paul,
For any educational institutions on this list - what has been the impact on your mail services once your ISP started blocking port 25 - what if any was the backlash - and how difficult was it to provide alternatives ...587,465 etc ...
Our ISPs don't filter our traffic. If they consistently did, they probably wouldn't be our ISPs for long. OTOH, the question that you didn't ask was if educational institutions themselves are blocking port 25 from their users :) In our case, yes we are. We only allow SMTP connections from our dorm subnets to the campus mail servers. Personally, I thought there was going to be a huge backlash from our community when we put this in about a year ago. Of the 12,000 students that this affected, I believe two have inquired about it but didn't really have an issue with it. Eric :)