Add an option to send an existing email to an appointment (Calendar Event).

Either right click on the email in a folder, or as an action (eg Move to Trash, Mark As Unread…) in the email view.

Add the email sender as a Recipient, and the mail title as the Appointment (Event) Title, and the email text as Description.

For example, receive an email about a new journal idea with copious detail, create a meeting appointment to discuss with automatic detail from the email.