Follow these steps in order one by one…
Open a new message.
Click ‘Format Text’ in the tabs at the top.
Left click on ‘Quick Styles’ so that it drops down.
Right click on ‘Normal’ and choose modify.
Where it says ‘Style for following paragraph’ choose ‘No Spacing’.
Then select the radio button below that says ‘New documents based on this
template’.
Click the little format button near the bottom of the dialog window and
select ‘Paragraph’ from the drop down.
On that new window, make sure line spacing is set to single.
Make sure the Spacing -> After value is set to 0pt.
Ensure that there is a check in the box that says ‘Don’t ass space
between……’
Say OK to that window.
Say OK to the window under it.
Close that new message.
Start a new message and try some typing …