There used to be an setting in the desktop version of Outlook that was on by default to remove extra blank lines (it’s been years, so I don’t remember the verbiage anymore). It was driving one of my clients CRAZY & once he changed it, emails from IS looked fine to him.
I have seen - even in gmail/google mail though that sometimes blank lines are removed. To solve this, I make sure that each line that I want left (like a break between paragraphs), I also insert a space and that seems to do the trick!!
On COMPLETELY different note - I’ve been on Colleen’s list for a couple of years and keep trying to get IS peeps to invite her to speak at an event! Love her quick videos!!