Why not put this in an append-only document that you can easily ctrl+a/c/v (or print) and move it as needed? Why would you want this kind of thing in email?
The act of drafting an email/letter is also emotionally distinct from appending to a text file. For example, in a text file, you are probably more likely to abbreviate your thoughts or omit pleasantries like "Dear son," / "Love, Dad." Each email is also timestamped in a way that's much more "provable" than text in your file, and also immune to edits after-the-fact.