Well, what I've done before is LrHttp.openUrlInBrowser( "mailto:firstname.lastname@example.org..." ), which doesn't inject any html but generally opens an email link... (can be called in response to text click or button click..).
Let us know if you discover anything better.
Ah, I see. I had been trying to feed it the string of a fully-formed HTML doc (<HTML> ... </HTML>) and not just the mailto link.
I agree with you that it'd be nice if something like this were better supported by the API (or at the very least, documented a bit better) but this is simple enough for the time being.
You can pass url parameters too, e.g.
local url = "mailto:email@example.com?subject=Subject&body=Body"
LrHttp.openUrlInBrowser( url )
But unless you know how to force html format (I dont), the body will be interpreted as plain text.
Also, beware of url-encoding - I'm not sure whether pre-encoding is required or not.