The only Hot Questions feed I can find is the central SE feed. This obviously contains every hot question for every site and every tag. But each item in the feed has enough information to work out what tags apply and what site which means you can process it down.
You could do this with any of a number of tools, but here's a nice simple Yahoo Pipes version:
You can create your own based on this or just use mine.
That still leaves you with an RSS feed and not an email but there are dozens of services (Pipes might even do it) that will forward an RSS result onto email:
Alternatively you could do the whole thing in a programming language without breaking much of a sweat.