"Paste without formatting" preserves line spacing
Hi!
If you "paste without formatting" some text in an email, the line spacing is preserved and there's no way to get rid of that other than pasting the original text into another text editor (like gedit) and then copy it from that application.
You should be able to easily replicate this by writing a few words/letters in libreoffice writer on several new lines, and then copy them all and "paste without formatting" into some email in geary.
I tested this in geary 3.34.2