Do emails whether read or unread, whether in inbox or folder take up storage?

Hi Sobernheim, thank you for posting in Apple Support Communities.

I do hope the above link has resolved your question.

However, you can also contact Apple Support if you have any further questions about storage as follows:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above but also again as follows Apple – Location Selector; or
• Using the "Apple Support" app, available and downloadable from App Store.