Ditto Rob. I run a mail server on a dynamic IP cable modem. Acceptable Use Policy doesn't say I can't. They were talking about blocking port 25 outbound which would stop this problem (different ISP though to the one in question) but as far as I am aware they haven't yet.

I think however they should block by default and then allow users to request ports be opened. That would at least stop the majority of the problem IMO. Some ISPs do that here already.

I'd also be pissed off if they blocked incoming ports since I run a webserver and SMTP server. An outgoing block on 25 is no big deal - I already send all mail via the ISPs mail server anyway.