Just FYI:
The Rich Text Editor has a very big problem: If JavaScript is disabled, it disappears ... completely without an alternative.
So, I found another workaround for me:
I added a hidden field (short name: "HTML_msg").
And I added a client side event (Advanced field options) to my multiline textbox (short name: "Text_msg"):
if ($(Text_msg).length > 0) {
var strHTML = $(Text_msg);
strHTML = strHTML.replace(/\r\n/g, '\n');
strHTML = strHTML.replace(/\r/g, '');
strHTML = strHTML.replace(/\n\n+/g, '\n\n');
strHTML = strHTML.replace(/\n/g, '<br /> \n');
$(HTML_msg) = strHTML;
}
It only works if JavaScript is enabled, but it's enough for me.
On submit my form is sending an email with both $(HTML_msg) and $(Text_msg).
If Javascript is disabled at client side, I just have the message without line breaks.
It's not the optimum, but better than nothing.