The easiest way to ensure that newlines are preserved is by making sure that the content you are sending has formatting that can not be captured in plain text alone. For instance, if the content has bullets, or if it has bold, italics, underline etc.
If you don’t want any of the text to be bold, you can just bold a blank space which will look similar to plain text visually but under the covers will not be stored as plain text. The following example document sends an email that preserves the new line. This is because there is a blank space after the character ‘b’ which has been bolded.
We will work on making this easier so you don’t have to do these workarounds, but this should help you in the meanwhile.