(with-eval-after-load 'notmuch
  (defun my-notmuch-query (sexp)
    "Return string query equivalent to SEXP."
    (format "sexp:\"%s\""
            (string-replace "\"" "\"\""
                            (format "%S" sexp)))))

(with-eval-after-load 'notmuch
  (unless (equal (notmuch-config-get "built_with.sexp_queries") "true")
    (user-error "Notmuch not built with sexps.")))