Cacher is the code snippet organizer for pro developers

<?php

/* The wp_mail_from filter modifies the "from email address" used in an email sent using the wp_mail function. 
 * auto-detect the server so you only have to enter the front/from half of the email address, including the @ sign 
 * https://codex.wordpress.org/Plugin_API/Filter_Reference/wp_mail_from
 */

function xyz_filter_wp_mail_from($email) {
    /* start of code lifted from wordpress core, at /wp-includes/pluggable.php */
    $sitename = strtolower($_SERVER['SERVER_NAME']);
    if (substr($sitename, 0, 4) == 'www.') {
        $sitename = substr($sitename, 4);
    }
    /* end of code lifted from wordpress core */
    $myfront = "whateverIwant@";
    $myback = $sitename;
    $myfrom = $myfront . $myback;
    return $myfrom;
}

add_filter("wp_mail_from", "xyz_filter_wp_mail_from");