It would be great if you inserted a screenshot of your client in action in the README.md. In my experience screenshots have excellent information density when it comes to evaluating software :)
2. Can you give me plain english instructions for composing plaintext emails by default?
Lumail is a console-based client, much like mutt. To compose an email your editor is launched. If no editor is configured vim will be used.
Plaintext composition is the only thing that is supported.
3. Does it hard-wrap your plaintext emails at 72 columns?
The mail client doesn't, since it opens a temporary file with your configured editor. You could configure your editor to enable/disable wrapping ..
4. Does it support format=flowed?
As above.
5. When replying to a message, does it put your reply above or below the quoted message you're repying to by default? Can you change this setting? How?
The editor opens a temporary file into which the quoted body of the mail you're replying to has been placed.
I configure my editor to be `vim +/^$ ++1` which puts the cursor above the mail, but below the headers.
You could do something similar to place the cursor at the bottom, but that would require a suitable editor-specific command to be set.
lumail, c++, gpl
https://github.com/lumail/lumail