I don't mean to "me too" without reason here...

I think I can explain the logic (we do this on our networks - both company, managed and ISP / ADSL services):

If I let people on my net go to 25 on other servers, they can attack their servers, search for open relays, and viruses that infect them are free to make connections out to other services and will spread more quickly. I'd suggest everyone should transparently capture port 25 wherever they can (a transparent proxy has the benefit of either redirecting the users to your server which will at least return an error message for their client to display, or selectively allowing relaying).

There are network security and reliability issues in letting 25 through - 587 doesn't have the same issues though due to the authentication requirement, and honestly I've NEVER seen a virus try to use it for this reason I guess.

Currently the ISP's (and from my experience the hotel's ISP's - the hotels themselves often do not have IT staff to manage a firewall!) have real reasons to do such blocking - there are numerous ways around it for anyone who runs their own server with their own roaming users though, so I don't see the problem lasting forever - once there are alternatives, consumer pressure will force the ISP neophytes into the modern world ;-)

m/