Using New Outlook on Windows for personal email, calendar, and contact management
Depends on what you want to do with the edit function. I used to be able to add in a note for sent invoices with a date of payment. To overcome the lack of editing I now forward the mail to myself, which allows text to be added. Not sure if you can delete stuff, I haven’t tried.
This is exactly my use case, and I use the same workaround. I only just found this thread, as I had assumed that it was my own ignorance that was hiding the "edit message" function from me. But apparently not!