RE: Marketing Email Type Styles
I have the same question like Samatha, where I have not understand the answer yet.
So I want to remove the fonts "Comic Sans MS" and "Courier New" from the InlineToolbar because they are not in my corporate style guide:

I have already tried it with the xml:
<meta type="xrm/designer/setting" name="remove-fonts" datatype="font" value="Comic Sans MS,Courier New">
but that was not working. (The opposite way of adding additional fonts like documented in https://docs.microsoft.com/en-us/dynamics365/marketing/custom-template-attributes#add-new-fonts-to-the-text-element-toolbar)
Does anyone know how to achieve that?
And the second issue was, that I have tried to edit the styles from the InlineToolbar, but also with no success:
I want to be able to select in the "Styles" only H1, h2, h3, and so on and also remove the stylings which I do not need:

And the third issue is also the same: how can I place the colors according to Corporate Style Guide in the color picker:

Thanks for your help in advance, Carolin