Spacing my paragraphs in the editor

This is a general question, not sure if it is related WP version or theme.

When I get a story via email, I copy if from my email program, paste it into my text editor, then copy again. The removes all the formatting, but leaves the paragraphs in place. When I paste it into the HTML editor, there are no spaces between paragraphs. So, I go through and insert two returns in between each paragraph. I think this makes it easier to read on the screen. What I would call double spacing.

Here is my question. Sometimes WP “fixes” these extra spaces by removing them, sometimes it does not. So what controls this behavior? How can I consistently get these double spaced paragraphs to stay.

TIA,
mark