Dec 12
I spent ages searching for this. I like to have my Sent folder on mac, with Apple Mail, contain both local messages on my computer and remote messages on the server. You get a nice hierarchy where, most of the time, a single “Sent” box holds all sent messages, but click the arrow next to it and you have your local sent messages and your remote sent messages separately.
It sounds simple, but it took me ten minutes to find. Just say in the imap settings to store sent messages on the server, then rename your local sent folder to “Sent” and the two will magically merge. No amount of dragging and dropping will get you there, though.