[jcfrei]

I'm not sure I understood you correctly. Are you saying it's a common thing for all "ISPs" in the US to block outgoing traffic on port 25 (and allow incoming traffic for Outlook et al.)? Or do you simply mean that most email providers will block incoming mails from residential IP adresses?

[sp332]

The first. I don't know exactly how many ISPs do it, but it's pretty common. http://www.vtdesignworks.com/blog/comcast-xfinity-port-25-bl...

[spc476]

My provider (BellSouth or AT&T or whatever they're calling themselves this week) block incoming port 25 and block outgoing to port 25 to anywhere except their SMTP servers, because of spam.