[Dba-office] Network not sending emails out of network

Here's a curious problem from a reader -- I don't think this is an Outlook
problem at all, but thought I'd ask around. Thanks for any potential
insight! -- Susan H.

Dear Susan,

   2 computers: 1 Dell desktop running Vista HP & Office 2007
                        1 Dell Laptop running Windows 7 & Office 2010
   1 ISP: Comcast Broadband

Problem: I have used Outlook for many years, both at work & home & love it.
Up until about 2 months ago, I have had no problems at all sending or
receiving from either computer via our Comcast accounts, as well as GMail.
For some reason, I discovered the hard way that, while I'm receiving about
everything that is sent to me, I can no longer send to any email address
other than within my own network. I cannot even send to my own GMail
account.

I've spent hours wt Comcast, bottom line: verified that I am able to send &
receive WITHIN my own accounts, but nothing outside Comcast.
I have followed a variety of directions, usually after searching boards for
help, as to how to configure Outlook properly for my situation and each
computer, again wt no improvement.

I'm baffled. For everything to have worked fine for years, and then all of
a sudden, to have lost 1 side of the equation--just doesn't add up! Any
comments, questions or suggestions are readily welcomed!

Thanks for whatever help you can provide!

(by the way, the Cc address above is our primary Comcast account address)