Why don't you just block the whole Internet?
I tried to send email today, but it wasn't working. Turns out Shaw started blocking port 25 (SMTP). Considering I have a business internet account with them, I was pretty upset, especially since I wasn't notified in advance. They said they sent an email months ago.
I asked them to give me details of the message (when, what was the subject, what was the from address?) so I could try to find it but the person didn't know that information. I would have expected a letter to be sent to my address for a change in service.
The only way around the block was to pay $20 a month for two static IP addresses.
So I asked my ISP if there was a workaround. Use port 2525, they said. Yup, that works.
As for .Mac, use port 587, that works.
What a stupid policy.