No.
The Comcast mail server is a POP server. An alternative that keeps all the connections synced would be an IMAP server. But that is not what Comcast provides.
When you use the Mail app on your iPhone or iPad, it downloads the mail for the Comcast server and either leaves it there or deletes it as you specify in the Mail app settings. (For all of my devices, I download messages and leave them. Only my desktop Mac deletes mail off the Comcast server when it fetches it.) So each device has its own collection of messages. As you are finding, that isn't optimal.
An alternative would be to use either the Xfinity Mobile app or the mobile version of SmartZone to directly access your Comcast email on the server. Any changes you made would be made on the server. So if you deleted a message, it would be deleted. This approach requires you to have an internet connection to read older stored email messages. But for many people that's a good solution.
One reason I use the Mail app approach is that I am grabbing mail from multiple servers and multiple accounts. I think I have seven mail accounts on my iPhone. That lets me check things while I'm out and about. Sometimes when I answer a question, I'll send myself a blind carbon copy so that it will get to my desktop. But my desktop is my main location.
