My company has comcast business broadband service, which is probably not related to the problem here: We host our own email. When we send email to recipients on comcast.net, it comes back as delayed or undeliverable. Comcast tech support tells me our IP is not on Comcast's "block list." I have been unable to determine why we cannot send email to comcast.net accounts. I'm reluctant to call Comcast tech support again, because the technicians who answer often know less than I do -- some don't even know what a static IP is, and others have insisted that the static IP config on our modem needs to be reconfigured (it doesn't) and when they attempt to re-build the file, we always lose all email service for hours, until I call repeatedly to have someone else repeat the process, correctly. Any help will be welcome.