Hello @Ihevsd ,
If you set your email's Design defaults for specific fonts, that will apply to any next blocks of the set type (text, article, header, etc.), as well as to any existing text blocks that haven't been manually set. If you're copying text from elsewhere, it's best to paste it in without formatting, or use a plain text editor to clear the copied formatting first, then copy that into the editor.
If you copy an email with particular design defaults, they will be carried over into the new copy. I'd recommend updating your reusable template(s) design defaults so they will carry over to any copies / new emails you make from them. If you don't already have a reusable template setup, then I'd advise doing so.
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