Hmmm. I switched in late December without the godawful software and didn't have this problem.
Did you reboot the router? It is possible that you'll have to clone the Mac address of the PC to the router, too, if that hasn't already been done. (Sorry if these are stupid suggestions, but I'm not that familiar with Netgear stuff.) I stuck the new Comcast userid in my router's 'pc-name' field but am not convinced that it was necessary. (I use an SMC, btw.)
I started a thread on this before Christmas where many savvy folks chimed in; you can find it
here. The mail servers will change name from something like 'mail' to 'mail.comcast.net'.
If shutting everything down and powering up doesn't work, perhaps the more knowledgeable folks in this forum can add their 2¢.