Yes, you can!
It's true that Yahoo! Mail now automatically saves an email you're working on as a draft, in case you happen to lose power or lose your connection to the internet. It's also true that Yahoo! Mail removes an auto-saved draft from your Drafts folder when you send it. But you can block that behavior and both Send and Save a message as a draft.
Hold down the shift button:
- when you click Send, or
- when you hold down Ctrl and press Enter (the keyboard shortcut for sending).
Shift + Send
Shift + Ctrl + Enter (on your keyboard).