Not necessarily for the Outlook users. The default setting of my Outlook was to ignore double line breaks and (paragraphs), which makes plain text mails less readable.

Same for me, I cannot think of the use case for this - maybe it was introduced in the embrace/extend/extinguish era to nudge people into using Rich Text format emails?

It is Outlook that is gross.

Unfortunately, sometimes in the real world we don't all get to always choose our own tools.

Sure, but you still shouldn't blame plain text for Outlook's failures.

I didn't lay blame at all. I just asked: "Do you wind up with plaintext emails that look gross when opened in Outlook?"

My presumption, based on your defensiveness/evasiveness, is that the answer is "yes."

Fine, but Outlook does not make plain text emails look nice.