I also had some configuration problems using Comcast SMTP. After much troubleshooting, the I traced the problem to the following configuration settings:
I use a wireless connection only. I am connected through an Apple Airport Extreme router.
I configured IPv4 manually. In my setup, I NEED TO ENTER my router's IP address in both the "Manual Default Gateway" and the "Manual Preferred DNS Server" fields. If either or both of these fields are BLANK, the SMTP connection fails. With both fields FILLED IN with my router's IP address, there is no problem using Comcast's SMTP server.
The SMTP server settings for Comcast that work for me are as follows:
SMTP Server: smtp.comcast.net
SMTP Port: 587
Always use secure connection (SSL/TLS): UNCHECKED
SMTP server requires authentication for outgoing e-mail messages: CHECKED
SMTP User ID: For me, the User Name alone, or the full email addtess both work - if you have trouble, try it each way...
I'm amazed at the conflicting settings that people say must be used. By having the Manual IP address fields blank, as a previous poster suggests, my ability to use Comcast's SMTP server was completely cut off. All I can say is look at the Embedded Web Server's Network settings page and try changing some options to see if it makes a difference.
