It’s easy, just remove all styling, all padding, all formatting and then throw in a few random mistakes and you’ll get close to what Lotus 6 and 7 users are seeing. For Lotus Notes 8 they seem to have come to their senses and most things render pretty well on it.
6 and 7 is a pain in the proverbial, you can code the strictest html email in the world and somehow Lotus will find a way to render it incorrectly. It can even change from send to send, one day it feels like rendering something correctly another day it doesn’t.