I found some code that seems to work.
It does not interfere with contact form 7.
/*
* Plugin Name: T5 Filter System From Mail
* Description: Sets the WP from mail address to the first admin’s mail and the from name to blog name.
* Plugin URI: https://toscho.de/?p=2201
* Version: 2012.08.30
* Author: Thomas Scholz
* Author URI: https://toscho.de
* License: MIT
*/
if ( ! function_exists( 't5_filter_system_from_mail' ) )
{
/**
* First admin's e-mail address or blog name depending on current filter.
*
* See wp-includes/pluggable.php::wp_mail()
*
* @param $input Name or email address
* @return string
*/
function t5_filter_system_from_mail( $input )
{
// not the default address, probably a comment notification.
if ( 0 !== stripos( $input, 'wordpress' ) )
return $input; // Not auto-generated
return get_option( 'wp_mail_from' === current_filter()
? 'admin_email' : 'blogname' );
}
add_filter( 'wp_mail_from', 't5_filter_system_from_mail' );
add_filter( 'wp_mail_from_name', 't5_filter_system_from_mail' );
}