I know it's possible to use CSS to add page breaks to web pages, for when they're printed.
I also know CSS support in HTML emails is poor.
So, is there a way to generate a page break when an HTML email is printed? Or given the variety of email clients out there, is that just a daft question?
I'd say do it the standard CSS way. It'll work for some e-mail reading agents. There's no other way to hint at page breaks. If it's really important that people can print the message then maybe make the message available through the web too and tell the recipient to print that one.
See this article on CSS support in HTML emails it gives a list of what is and what is not possible.