How to preserve multiline TextBox/RichTextBox new lines in HTML mail body

Question

I am trying to preserve new lines from RichTextBox (or normal TextBox if RTB will not work) while copying the RichTextBox.Text to HTML body in my Outlook mail.

I have tried many things over last couple of hours and nothing works.

I store RichTextBox text in variable like that:

Dim msg as string = RichTextBox.Text

Then I tried many things, like using Replace():

msg = msg.Replace(Environment.NewLine, "<br>")

or other things (or other characters "\r\n") etc. and nothing works. The msg string when copied into Outlook HTMLbody is in one line without any change.

What am I missing in here? I have looked over SO for a few hours today and cannot find a solution.