What happens when the photos are on Google Photos? What happens when they need to update their browser because theirs is outdated and becomes incompatible? What happens when one of their grandchildren sends them a YouTube link to their concert performance from school? I absolutely guarantee you that in each of these scenarios they will call and complain because their email isn't working.
They think that they only want email, but what they really want is to access the internet via their email.
So not only do you want to snoop your legitimate customer's traffic, you also want to own their personal computers at a level that would allow you to make that distinction? I find that disgusting.
Also, I don't think I've ever heard such a misuse of the word "simply"
>To eliminate support calls I would simply design a system where any place they went FROM their email would work - maybe up to 3 or 4 links past email.
What? What constitutes a "link"? This doesn't make any sense.
How are you determining this without sniffing everyone's traffic? How do you know if someone typed youtube.com into their browser window or clicked a link from an email without access to things like referral headers?
