Comcast and Port 25 Blocking

[Matthew Gillen]

bill at horne.net wrote:
> Conclusion: I think Comcast has some automated system that blocks port 25
> based on criteria they don't want to reveal. The guy I talked to said 
> any blocking happens at the cable modem, so I don't know if changing the 
> MAC address so as to get a different IP would make any difference.

I know (from looking at my mail server's logs) they run relay tests once
a month or so to see if your server is an open relay.  I don't know if
they do anything more sophisticated.
--Matt