+1. Emacs variable `message-send-mail-function` has not been set
+
+ Initially, Emacs variable `message-send-mail-function` has value of
+ `sendmail-query-once`. When (notmuch) message mode is about to send email,
+ `sendmail-query-once` will ask how emacs should send email. Typing `smtp`
+ will configure `smtpmail` and Emacs may prompt for SMTP settings.