Your email body has certainly the HTML tag <PRE> which indicates 'preformatted text', generally it used to fix the space to simulate column in text mode. By default, Automatic Email Manager is compliant with PRE tag, but you can disable it if your text looks small because the width is too large for page, just go in the options (click on menu 'File', then 'Options'), now go in the section 'Advanced' and now unset the option 'Enable the HTML tag PRE...'.

Options to render html PRE