Comcast email on iPhone won't synch with other devices

My Comcast email on my iPhone won't synch with my Mac, or iPad. I AM ABLE to send and receive messages on ALL devices, however iPhone will not show emails as read or won't delete (if viewed and deleted on Mac or iPad). I have tried clearing cache, deleting cookies, removing and reinstalling Apple's mail app (which has my Comcast email on it), all to no avail. I hate deleting everything twice. Can someone give me any suggestions?