+CUSTOM COMMANDS
+---------------
+
+If the given command is not known to notmuch, notmuch tries to execute
+the external **notmuch-<subcommand>** in ${PATH} instead. This allows
+users to have their own notmuch related tools to be run via the
+notmuch command. By design, this does not allow notmuch's own commands
+to be overriden using external commands.
+