Salesforce is gently pushing us to use Files and not Attachments. However, in Classic I seem unable to prevent the creation of new Attachments. In Setup, there is the option "Files uploaded to the Attachments related list on records are uploaded as Salesforce Files, not as attachments", but this does not seem to have any effect on emails.
Even if I select a File (not an Attachment) and I send it by email, from the Classic Salesforce UI, a new Attachment is created. I check this via a query on the Attachment object. In Lightning it is working correctly, the File is shared with the new email, no Attachment is created.
How to prevent this?