There's not currently a way to automatically add the appeal to the user's record after they receive the email. You would need to review the email reporting to see who received the email, and then manually add the appeal through The Raiser's Edge. If you're using Constituent Queries for the messages, you may be able to setup a query based system that pulls in who received the email, and then batch add an appeal.

How to add or remove an appeal or source to a donation form