In the happy world of computers there are two kinds of returns/line breaks.
Hard return and Soft return.
This applies not only for the newsletter, but also in Word and other programs as well.
Hard return is when you just press Enter. Then you say to the background code that you want to end the text paragraph you worked in and want to start a new one.
Depending on the settings of the template you are working with, you can get a bigger line spacing.
Soft return is when you hold down the Shift key while you’re pressing Enter. Then you say to the background code that you want to remain in the text paragraph you are working in right now, but you want a simple line break. Then there will be no extra spacing between the lines.
Avoid trying to force the text to make a line break using the space bar. In the background, your newsletters use HTML code, and in HTML two spaces or more consecutively becomes a code called non-breaking-space. This code can be interpreted differently between different browsers, and your text can look good on your computer, but strange on another.
So overall when working with HTML, if it’s in newsletters or on websites or elsewhere, you should avoid making two spaces (or more) after one another. It can cause trouble for you.