Oops, left my computer for a while. Here's my work on the html email so far. There's nothing fancy about it - just text. The main difference between this and a plain text email though is that it is anchored so that you can go directly to the language version you prefer. It also gives a nicer layout of links.
I'm sorry if my initial reply to Tony was a bit abrupt - I still think that quarto-l is where this should be discussed, but I appreciate the opinions. Any replies to my initial query, ie why this version doesn't work?
Cormac