A while back I posted about Comcast blocking outgoing traffic on port 25. We've spent some time with Verizon's DSL service, but after our recent move we're back with Comcast. Luckily, Comcast now explicitly lists the ports they block. Nothing I care about, except for port 25 (incoming and outgoing). For incoming mail, I use Dyn to forward mail to port 587. For outgoing mail, I had been using stunnel through outgoing.verizon.net for my SMTP connections. Comcast takes a similar approach forcing outgoing mail through port 465 on smtp.comcast.net.