Don't use HTML5 form validation in config manager
E. g. Firefox prevents entering "@NAME@ (@USER@) <@MAIL@>" info the mailfrom option through the configuration manager. A small popup appears saying "Please enter an email address."
As the configuration plugin also handles invalid inputs, the HTML5 validation should be disabled.
https://github.com/splitbrain/dokuwiki/blob/master/lib/plugins/config/settings/config.class.php#L751
http://www.the-art-of-web.com/html/html5-form-validation/#section_1