This is working for pasting from Safari into Mail, except for line-spacing: if the lines on a website have space between them, they'll be spaced out when pasted via this method. For example, this text from a forum post has spacing between the lines because of the margin styling (specifically, the margin-block-start and margin-block-end properties):
It looks like this when pasted into Mail with a macro that uses the "Apply Style to Clipboard" action, with the font set to 14 point Georgia:
And, in Mail, it is impossible to adjust line-spacing, so I'm stuck with it. You mention that Mail uses Rich Text for stying, and indeed, when I paste the above into TextEdit, the "Line and paragraph spacing" information looks like this:
Does anyone have an idea about how to address this? It would be great if the "Apply Style to Clipboard" action had options for line-spacing, but it doesn't seem to.