Force the default from e-mail address

functions.php

add_filter( 'wp_mail_from', 'bk_force_default_email', 1 );

function bk_force_default_email(){
  $sitename = strtolower( $_SERVER['SERVER_NAME'] );
  if ( substr( $sitename, 0, 4 ) == 'www.' ) {
    $sitename = substr( $sitename, 4 );
  }
  
  $email = 'wordpress@' . $sitename;
  return $email;
}