Hello,
How come that when you write a new mail or reply to a mail
the text you enter is by default formatted in doubble-line?
I would prefer that it was formatted in single-line so I didn't
have to hold down the Shift key + Enter every time I want to
make a soft line break. As far as I can see I can not change this
formatting in the settings.
Its how TinyMCE is setup not RoundCube, there was some TinyMCE config options you could tweak to change that but I can't remember what they where.
TinyMCE is the HTML editor that Roundcube uses. A couple of years ago, I looked into changing that behavior, but I found that TinyMCE developers don't like single-spacing, and the feature was not well supported, and it was buggy. I don't know if that is still the case. Try Googling TinyMCE for more details.