I understand creating a Visualforce Email template that adds the Email as an Attachment but how does one add that Email Attachment back to the Related Object type that the email is being sent from?

Email attachments are not seen on the Object and we want to be able to make sure we can view the Attachments that have been sent via email on the actual Object. For example: You are sending an email from an Opportunity and the email generates a PDF attachment to send with the email, but you want to see that same attachment appear as an Attachment related list item on the Opportunity.

Can someone point me to the right info to do this please?

Thanks.