I'll be posting about this but we removed the spell check button b/c the service it uses has been discontinued by google. We will be making some changes to make the web browser spell check work nicely inside the editor (specifically for Chrome). Firefox works well today, as long as you have spell check turned on.
I too thought I went crazy today looking for the spell check button on email editor.
I use Firefox and have "check spelling when you type" but Marketo email editor doesn't pick up and identify these in the email editor. Is there something that I am missing?
I will be posting an article on how to do this. For Firefox, make sure you have "Check my spelling as I type" selected under preferences. Then, in the editor, right click on a word an make sure "Check Spelling" is on.
Google discontinued their service, so you will notice that it doesn't work well in Chrome. You have to select a word and then right click and run the spell check on that word. The fix we are putting in for July will make this a better experience. I am posting a discussion shortly with instructions.