I will add the link unlink to the newsletter toolbar, that was intended to be included.
Unfortunately the spellchecker was based on google's spell checking api which has been permanently discontinued.
However, if you remove spellchecker from the plugins list for all of the toolbars (as I have done just now in the master copy of mojoTinyMCE4.config), you will find that the web browser spellchecker will squigly underline unrecognized words (at least in Chrome which I am using). If you hold down control and right click the squigly word it will suggest a spelling.
Hope that helps,