Query Output Window not honoring fixed length
It is honoring the fixed character length.  However, it does not appear to be using a monospaced font so it looks like it isn't.  The character length is fixed for the column.  The character width is font dependent.  DB Mail is using a monospaced font.

https://en.wikipedia.org/wiki/Monospaced_font


  A monospaced font, also called a fixed-pitch, fixed-width, or
  non-proportional font, is a font whose letters and characters each
  occupy the same amount of horizontal space.[1] This contrasts with
  variable-width fonts, where the letters and spacings have different
  widths.


Notice that the space taken up by an M is more than taken up by an I